Mark expect/actual classifiers as experimental

^KT-61573 Fixed
Review: https://jetbrains.team/p/kt/reviews/11969/timeline

Tests:
- MultiPlatformIntegrationTestGenerated
- CliTestGenerated
- MultiPlatformIntegrationTestGenerated
- DiagnosticTestGenerated.Multiplatform
- FirLightTreeOldFrontendDiagnosticsTestGenerated

Also add -Xexpect-actual-classes flag to all necessary ./libraries/* modules
Otherwise compilation of those modules failes because of `-Werror`

compiler/testData/multiplatform/classScopes/constructorIncorrectSignature/output.txt

@@ -1,6 +1,9 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/constructorIncorrectSignature/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo {
+^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/output.txt

@@ -1,6 +1,24 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect enum class AB { A, B }
+^
+compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/common.kt:1:24: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect enum class AB { A, B }
+                       ^
+compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/common.kt:1:27: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect enum class AB { A, B }
+                          ^
+compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/common.kt:3:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect enum class CD { C, D }
+^
+compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/common.kt:3:24: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect enum class CD { C, D }
+                       ^
+compiler/testData/multiplatform/classScopes/enumsWithDifferentEntries/common.kt:3:27: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect enum class CD { C, D }
+                          ^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/fakeOverrides/output.txt

@@ -1,7 +1,25 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/fakeOverrides/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect open class Base {
+^
+compiler/testData/multiplatform/classScopes/fakeOverrides/common.kt:5:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Derived : Base {
+^
 
 -- JVM --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/fakeOverrides/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect open class Base {
+^
+compiler/testData/multiplatform/classScopes/fakeOverrides/common.kt:5:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Derived : Base {
+^
+compiler/testData/multiplatform/classScopes/fakeOverrides/jvm.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+actual open class Base {
+^
+compiler/testData/multiplatform/classScopes/fakeOverrides/jvm.kt:5:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+actual class Derived : Base() {
+^

compiler/testData/multiplatform/classScopes/functionAndPropertyWithSameName/output.txt

@@ -1,6 +1,9 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/functionAndPropertyWithSameName/common.kt:3:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo {
+^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/functionIncorrectSignature/output.txt

@@ -1,6 +1,9 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/functionIncorrectSignature/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo {
+^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/functionIncorrectSignatureFromSuperclass/output.txt

@@ -1,6 +1,9 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/functionIncorrectSignatureFromSuperclass/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo {
+^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/missingConstructor/output.txt

@@ -1,6 +1,9 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/missingConstructor/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo {
+^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/missingFunction/output.txt

@@ -1,6 +1,9 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/missingFunction/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo {
+^
 
 -- JVM --
 Exit code: COMPILATION_ERROR

compiler/testData/multiplatform/classScopes/simple/output.txt

@@ -1,8 +1,16 @@
 -- Common --
 Exit code: OK
 Output:
+compiler/testData/multiplatform/classScopes/simple/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo(param: String) {
+^
 
 -- JVM --
 Exit code: OK
 Output:
-
+compiler/testData/multiplatform/classScopes/simple/common.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+expect class Foo(param: String) {
+^
+compiler/testData/multiplatform/classScopes/simple/jvm.kt:1:1: warning: the expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature. You can use -Xexpect-actual-classes flag to suppress this warning.
+actual class Foo actual constructor(param: String) {
+^