[K/N] Mark Platform-related API with ExperimentalNativeApi

As part of stabilizing Native stdlib.

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

@@ -4,6 +4,7 @@
  */
 package kotlin.native
 
+import kotlin.experimental.ExperimentalNativeApi
 import kotlin.native.internal.GCUnsafeCall
 import kotlin.native.internal.TypedIntrinsic
 import kotlin.native.internal.IntrinsicType
@@ -11,6 +12,7 @@ import kotlin.native.internal.IntrinsicType
 /**
  * Operating system family.
  */
+@ExperimentalNativeApi
 public enum class OsFamily {
     UNKNOWN,
     MACOSX,
@@ -26,6 +28,7 @@ public enum class OsFamily {
 /**
  * Central Processor Unit architecture.
  */
+@ExperimentalNativeApi
 public enum class CpuArchitecture(val bitness: Int) {
     UNKNOWN(-1),
     ARM32(32),
@@ -41,6 +44,7 @@ public enum class CpuArchitecture(val bitness: Int) {
  * Memory model.
  */
 // NOTE: Must match `MemoryModel` in `Memory.h`
+@ExperimentalNativeApi
 public enum class MemoryModel {
     STRICT,
     RELAXED,
@@ -50,6 +54,7 @@ public enum class MemoryModel {
 /**
  * Object describing the current platform program executes upon.
  */
+@ExperimentalNativeApi
 public object Platform {
     /**
      * Check if current architecture allows unaligned access to wider than byte locations.
@@ -125,7 +130,6 @@ public object Platform {
      * `KOTLIN_NATIVE_AVAILABLE_PROCESSORS` environment variable. When the variable is set and contains a value that is not
      * positive [Int], [IllegalStateException] will be thrown.
      */
-    @ExperimentalStdlibApi
     public fun getAvailableProcessors() : Int {
         val fromEnv = Platform_getAvailableProcessorsEnv()
         if (fromEnv == null) {

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

@@ -33,6 +33,7 @@ public class MutableData constructor(capacity: Int = 16) {
 
     private var buffer_ = ByteArray(capacity).apply { share() }
     private var buffer: ByteArray
+        @OptIn(ExperimentalNativeApi::class)
         get() =
             when (kotlin.native.Platform.memoryModel) {
                 kotlin.native.MemoryModel.EXPERIMENTAL -> buffer_

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

@@ -5,6 +5,7 @@
 
 package kotlin.native.concurrent
 
+import kotlin.experimental.ExperimentalNativeApi
 import kotlin.native.internal.ExportForCppRuntime
 import kotlin.native.internal.Frozen
 import kotlin.native.internal.VolatileLambda
@@ -137,6 +138,7 @@ public value class Worker @PublishedApi internal constructor(val id: Int) {
      * @throws [IllegalArgumentException] on negative values of [afterMicroseconds].
      * @throws [IllegalStateException] if [operation] parameter is not frozen and worker is not current.
      */
+    @OptIn(ExperimentalNativeApi::class)
     public fun executeAfter(afterMicroseconds: Long = 0, operation: () -> Unit): Unit {
         val current = currentInternal()
         if (Platform.memoryModel != MemoryModel.EXPERIMENTAL && current != id && !operation.isFrozen) throw IllegalStateException("Job for another worker must be frozen")