Warn on for-in-array range variable assignment in loop body

According to KT-21354, this should be a warning in 1.2 and before, and
no warning (with changed semantics) in 1.3 and later.
NB there are some false positives in this check.

 #KT-21354 In Progress
 #KT-21321 In Progress

compiler/testData/diagnostics/testsWithStdLib/forInArrayLoop/rangeVariableAssignment13.kt

@@ -0,0 +1,19 @@
+// !LANGUAGE: +ProperForInArrayLoopRangeVariableAssignmentSemantic
+// !DIAGNOSTICS: -UNUSED_VALUE
+// SKIP_TXT
+
+fun testObjectArray() {
+    var xs = arrayOf("a", "b", "c")
+    for (x in xs) {
+        println(x)
+        xs = arrayOf("d", "e", "f")
+    }
+}
+
+fun testPrimitiveArray() {
+    var xs = intArrayOf(1, 2, 3)
+    for (x in xs) {
+        println(x)
+        xs = intArrayOf(4, 5, 6)
+    }
+}