Stabilize unsigned types KT-45653

Deprecate specialized unsigned iterators for removal.

Fix compiler tests:
- drop unsignedLiteralsOn1_2 because apiVersion 1.2 is no longer supported
- drop experimental unsigned literals diagnostic test

libraries/stdlib/unsigned/src/kotlin/ULongArray.kt

@@ -41,8 +41,9 @@ internal constructor(@PublishedApi internal val storage: LongArray) : Collection
     public override val size: Int get() = storage.size
 
     /** Creates an iterator over the elements of the array. */
-    public override operator fun iterator(): ULongIterator = Iterator(storage)
+    public override operator fun iterator(): kotlin.collections.Iterator<ULong> = Iterator(storage)
 
+    @Suppress("DEPRECATION_ERROR")
     private class Iterator(private val array: LongArray) : ULongIterator() {
         private var index = 0
         override fun hasNext() = index < array.size