Mark all Worker-related API as obsolete.

* Explain what obsolete means and why workers are obsolete
* Add some documentation to workers to explain its common pitfalls

^KT-54702


Merge-request: KT-MR-9563
Merged-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>

kotlin-native/backend.native/tests/runtime/workers/mutableData1.kt

@@ -1,4 +1,4 @@
-@file:OptIn(FreezingIsDeprecated::class)
+@file:OptIn(FreezingIsDeprecated::class, ObsoleteWorkersApi::class)
 package runtime.workers.mutableData1
 
 import kotlin.native.concurrent.*
@@ -45,4 +45,4 @@ private fun assertContentsEquals(expected: ByteArray, actual: MutableData) {
     expected.forEachIndexed { index, byte ->
         assertEquals(byte, actual.get(index))
     }
-}
+}