Explicitly declare stability levels of declarations in kotlinx.cinterop package

* @ExperimentalForeignApi for all declarations that operate on
    unmanaged memory (i.e. pointers and references)
* @BetaInteropApi for the rest of the interoperability declarations,
    namely Swift/CInterop-specific interfaces and convenience-functions

### Implementation details

* Some typealiases are not marked explicitly because it crashes the compiler,
    yet their experimentality is properly propagated
* License header is adjusted where it previously had been existing
* Deprecated with ERROR interop declarations that are deprecated for more than
    two years are removed
* WASM target interop declarations are deprecated
* Deliberately make Boolean.toByte and Byte.toBoolean foreign-experimental to scare
    people away

^KT-57728 fixed

Merge-request: KT-MR-9788
Merged-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>

kotlin-native/backend.native/tests/codegen/intrinsics/interop_sourceCodeStruct.kt

@@ -1,3 +1,6 @@
+@file:Suppress("INVISIBLE_MEMBER", "INVISIBLE_REFERENCE")
+@file:OptIn(kotlinx.cinterop.ExperimentalForeignApi::class, kotlin.native.internal.InternalForKotlinNative::class)
+
 package codegen.intrinsics.interop_sourceCodeStruct
 
 import kotlinx.cinterop.*
@@ -5,8 +8,8 @@ import kotlinx.cinterop.internal.*
 import kotlin.test.*
 
 // Just making sure this doesn't get accidentally forbidden or otherwise broken.
-// (however defining structs this way is still strongly discouraged, please define
-// structs in C headers or .def files instead).
+// Used by auto-generated code, user-defined structs should be declared via
+// structs in C headers or .def files instead.
 
 @CStruct("struct { int p0; int p1; }")
 class S(rawPtr: NativePtr) : CStructVar(rawPtr) {