Native: represent ExperimentalForeignApi in cinterop's Stub IR

cinterop tool should add ExperimentalForeignApi to all generated
declarations by default. This commit supports this annotation in
cinterop intermediate representation -- Stub IR.

^KT-58362

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/KotlinCodeModel.kt

@@ -224,6 +224,8 @@ object KotlinTypes {
 
     val cValue by InteropClassifier
 
+    val experimentalForeignApi by InteropClassifier
+
     private open class ClassifierAtPackage(val pkg: String) {
         operator fun getValue(thisRef: KotlinTypes, property: KProperty<*>): Classifier =
                 Classifier.topLevel(pkg, property.name.replaceFirstChar(Char::uppercaseChar))

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/StubIr.kt

@@ -264,6 +264,8 @@ sealed class AnnotationStub(val classifier: Classifier) {
     class CEnumVarTypeSize(val size: Int) :
             AnnotationStub(Classifier.topLevel(cinteropInternalPackage, "CEnumVarTypeSize"))
 
+    object ExperimentalForeignApi : AnnotationStub(KotlinTypes.experimentalForeignApi)
+
     private companion object {
         val cCallClassifier = Classifier.topLevel(cinteropInternalPackage, "CCall")
 

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/StubIrMetadataEmitter.kt

@@ -444,6 +444,7 @@ private class MappingExtensions(
             )
             is AnnotationStub.CStruct.CPlusPlusClass -> emptyMap()
             is AnnotationStub.CStruct.ManagedType -> emptyMap()
+            is AnnotationStub.ExperimentalForeignApi -> emptyMap()
         }
         return KmAnnotation(classifier.fqNameSerialized, args)
     }

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/StubIrTextEmitter.kt

@@ -4,7 +4,6 @@
  */
 package org.jetbrains.kotlin.native.interop.gen
 
-import kotlinx.cinterop.ExperimentalForeignApi
 import org.jetbrains.kotlin.native.interop.gen.jvm.KotlinPlatform
 import org.jetbrains.kotlin.native.interop.indexer.*
 import org.jetbrains.kotlin.utils.addIfNotNull
@@ -506,6 +505,8 @@ class StubIrTextEmitter(
             "@Deprecated(${annotationStub.message.quoteAsKotlinLiteral()}, " +
                     "ReplaceWith(${annotationStub.replaceWith.quoteAsKotlinLiteral()}), " +
                     "DeprecationLevel.${annotationStub.level.name})"
+        is AnnotationStub.ExperimentalForeignApi ->
+            "@${KotlinTypes.experimentalForeignApi.topLevelName}"
         is AnnotationStub.CEnumEntryAlias,
         is AnnotationStub.CEnumVarTypeSize,
         is AnnotationStub.CStruct.MemberAt,