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/UIntRange.kt

@@ -14,8 +14,8 @@ import kotlin.internal.*
 /**
  * A range of values of type `UInt`.
  */
-@SinceKotlin("1.3")
-@ExperimentalUnsignedTypes
+@SinceKotlin("1.5")
+@WasExperimental(ExperimentalUnsignedTypes::class)
 public class UIntRange(start: UInt, endInclusive: UInt) : UIntProgression(start, endInclusive, 1), ClosedRange<UInt> {
     override val start: UInt get() = first
     override val endInclusive: UInt get() = last
@@ -47,8 +47,8 @@ public class UIntRange(start: UInt, endInclusive: UInt) : UIntProgression(start,
 /**
  * A progression of values of type `UInt`.
  */
-@SinceKotlin("1.3")
-@ExperimentalUnsignedTypes
+@SinceKotlin("1.5")
+@WasExperimental(ExperimentalUnsignedTypes::class)
 public open class UIntProgression
 internal constructor(
     start: UInt,
@@ -75,7 +75,7 @@ internal constructor(
      */
     public val step: Int = step
 
-    override fun iterator(): UIntIterator = UIntProgressionIterator(first, last, step)
+    final override fun iterator(): Iterator<UInt> = UIntProgressionIterator(first, last, step)
 
     /** 
      * Checks if the progression is empty.
@@ -113,7 +113,7 @@ internal constructor(
  * @property step the number by which the value is incremented on each step.
  */
 @SinceKotlin("1.3")
-@ExperimentalUnsignedTypes
+@Suppress("DEPRECATION_ERROR")
 private class UIntProgressionIterator(first: UInt, last: UInt, step: Int) : UIntIterator() {
     private val finalElement = last
     private var hasNext: Boolean = if (step > 0) first <= last else first >= last