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

compiler/testData/diagnostics/testsWithStdLib/annotations/jvmField/jvmFieldApplicability.kt

@@ -136,7 +136,7 @@ object IObject {
     val c: Foo = Foo(42)
 
     <!INAPPLICABLE_JVM_FIELD!>@JvmField<!>
-    val u = <!EXPERIMENTAL_UNSIGNED_LITERALS!>42u<!>
+    val u = 42u
 
     <!INAPPLICABLE_JVM_FIELD!>@JvmField<!>
     private val r: Result<Int> = TODO()