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/config/src/org/jetbrains/kotlin/config/AnalysisFlags.kt

@@ -54,6 +54,9 @@ object AnalysisFlags {
     @JvmStatic
     val builtInsFromSources by AnalysisFlag.Delegates.Boolean
 
+    @JvmStatic
+    val muteExpectActualClassesWarning by AnalysisFlag.Delegates.Boolean
+
     @JvmStatic
     val allowFullyQualifiedNameInKClass by AnalysisFlag.Delegates.Boolean