[K/N] Mark Any?.identityHashCode() as experimental

As part of stabilizing Native stdlib.

kotlin-native/runtime/src/main/kotlin/kotlin/Any.kt

@@ -36,6 +36,7 @@ public open class Any {
      * * Whenever it is invoked on the same object more than once, the `hashCode` method must consistently return the same integer, provided no information used in `equals` comparisons on the object is modified.
      * * If two objects are equal according to the `equals()` method, then calling the `hashCode` method on each of the two objects must produce the same integer result.
      */
+    @OptIn(ExperimentalStdlibApi::class)
     public open fun hashCode(): Int = this.identityHashCode()
 
     /**

kotlin-native/runtime/src/main/kotlin/kotlin/native/Runtime.kt

@@ -111,5 +111,6 @@ public external fun terminateWithUnhandledException(throwable: Throwable): Nothi
  * Compute stable wrt potential object relocations by the memory manager identity hash code.
  * @return 0 for `null` object, identity hash code otherwise.
  */
+@ExperimentalStdlibApi
 @GCUnsafeCall("Kotlin_Any_hashCode")
 public external fun Any?.identityHashCode(): Int

kotlin-native/runtime/src/main/kotlin/kotlin/native/concurrent/Internal.kt

@@ -109,6 +109,7 @@ internal fun ThrowFreezingException(toFreeze: Any, blocker: Any): Nothing =
 
 @ExportForCppRuntime
 @FreezingIsDeprecated
+@OptIn(ExperimentalStdlibApi::class)
 internal fun ThrowInvalidMutabilityException(where: Any): Nothing {
     val description = debugDescription(where::class, where.identityHashCode())
     throw InvalidMutabilityException("mutation attempt of frozen $description")