[FE] Type-safety refactoring: Make areCompatibleClassScopes to return Incompatible.WeakIncompatible

Review: https://jetbrains.team/p/kt/reviews/11039/timeline

For StrongIncompatible `actual` declaration is considered as overload
and error reports on expected declaration. For WeakIncompatible the
error is reported straight away

Before the refactoring `areCompatibleClassScopes` returned just
`Incompatible`. It is bad because StrongIncompatible isn't possible for
classes (classes can't be overloaded). Now all class incompatibilities
are weak.

The commit has a minor impact on observable behavior (cases where we
reported the compilation problems are still reported but on another
elements):
- We no longer report type parameter class incompatibilities on expect
  declaration, we report them only on actuals (it happened because all
  WeakIncompatible are reported only on actuals)
- In a sense, Java implicit actualization was the only way to "overload"
  classes (it would be a redeclaration compilation problem, so it
  doesn't count as a valid "overload"). And since type parameters
  incompatibility was StrongIncompatible for classes, we counted them as
  "overloads" and didn't report incompatibility problems on Kotlin
  class. Now we do report. (see
  implicitJavaActualization_multipleActuals)

compiler/testData/diagnostics/tests/multiplatform/java/implicitJavaActualization_multipleActuals.kt

@@ -1,7 +1,7 @@
 // MODULE: m1-common
 // FILE: common.kt
 
-expect class <!IMPLICIT_JVM_ACTUALIZATION{JVM}!>Foo<!>(i: Int) {
+expect class <!AMBIGUOUS_ACTUALS{JVM}, IMPLICIT_JVM_ACTUALIZATION{JVM}!>Foo<!>(i: Int) {
     fun <!AMBIGUOUS_ACTUALS{JVM}!>foo<!>()
 }
 
@@ -15,6 +15,6 @@ public class Foo {
 
 // FILE: jvm.kt
 
-class Foo<T>(t: T) {
+class <!ACTUAL_MISSING!>Foo<!><T>(t: T) {
     fun foo() {}
 }

compiler/testData/diagnostics/tests/multiplatform/kt54827.kt

@@ -1,6 +1,6 @@
 // MODULE: m1-common
 // FILE: common.kt
-expect class SomeClass<!NO_ACTUAL_FOR_EXPECT{JVM}!><T><!> {
+expect class SomeClass<T> {
     fun foo()
 }