Native: add detachObjCObject internal function for Obj-C objects

For a Kotlin wrapper of an Objective-C object, this functions zeroes
and releases the strong reference from the Kotlin wrapper to the
Objective-C object.
Usually, such a release happens only when the Kotlin wrapper is GCed.
So using this function can help that happen sooner.

^KT-59134

kotlin-native/Interop/Runtime/src/native/kotlin/kotlinx/cinterop/internal/Internal.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlinx.cinterop.internal
+
+import kotlin.native.internal.GCUnsafeCall
+import kotlin.native.internal.InternalForKotlinNative
+import kotlinx.cinterop.BetaInteropApi
+import kotlinx.cinterop.ObjCObject
+
+/**
+ * Detaches the Objective-C object from this Kotlin wrapper. More specifically, releases the Obj-C reference and zeroes
+ * the field where it is stored.
+ *
+ * This doesn't affect other possible Kotlin wrappers of this Objective-C object. Typically, when an Objective-C
+ * object gets into Kotlin, a new Kotlin wrapper is created, even if there is another wrapper already exists. To get
+ * the Objective-C object actually deallocated, each Kotlin wrapper should first be either GCed or detached with this
+ * function.
+ *
+ * If you use this object (Kotlin wrapper) after calling this function, the program behavior is undefined.
+ * In particular, it can crash.
+ */
+@InternalForKotlinNative
+@GCUnsafeCall("Kotlin_objc_detachObjCObject")
+@OptIn(BetaInteropApi::class)
+public external fun detachObjCObject(obj: ObjCObject)