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/cli/cli-common/gen/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArgumentsCopyGenerated.kt

@@ -31,6 +31,7 @@ fun copyCommonCompilerArguments(from: CommonCompilerArguments, to: CommonCompile
     to.effectSystem = from.effectSystem
     to.enableBuilderInference = from.enableBuilderInference
     to.enableSignatureClashChecks = from.enableSignatureClashChecks
+    to.expectActualClasses = from.expectActualClasses
     to.expectActualLinker = from.expectActualLinker
     to.experimental = from.experimental?.copyOf()
     to.explicitApi = from.explicitApi

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArguments.kt

@@ -632,6 +632,17 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
             field = value
         }
 
+    @Argument(
+        value = "-Xexpect-actual-classes",
+        description = "The expect/actual classes (including interfaces, objects, annotations, enums, actual typealiases) are an experimental feature.\n" +
+                "Kotlin reports a warning every time you use them. You can use this flag to mute the warning."
+    )
+    var expectActualClasses = false
+        set(value) {
+            checkFrozen()
+            field = value
+        }
+
     @Argument(
         value = "-Xunrestricted-builder-inference",
         description = "Eliminate builder inference restrictions like allowance of returning type variables of a builder inference call"
@@ -796,6 +807,7 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
             put(AnalysisFlags.extendedCompilerChecks, extendedCompilerChecks)
             put(AnalysisFlags.allowKotlinPackage, allowKotlinPackage)
             put(AnalysisFlags.builtInsFromSources, builtInsFromSources)
+            put(AnalysisFlags.muteExpectActualClassesWarning, expectActualClasses)
             put(AnalysisFlags.allowFullyQualifiedNameInKClass, true)
             put(AnalysisFlags.dontWarnOnErrorSuppression, dontWarnOnErrorSuppression)
         }