Cache array length in for-in-array loop if possible

If the range expression is not a local variable (which can be updated in
the loop body affecting loop behavior, see KT-21354), we can cache the
array length, thus turning a for-in-array loop into a simple optimizable
counter loop.

 #KT-21321 In Progress

compiler/testData/codegen/box/ranges/forInArrayWithArrayPropertyUpdatedInLoopBody.kt

@@ -0,0 +1,12 @@
+// WITH_RUNTIME
+
+var xs = intArrayOf(1, 2, 3)
+
+fun box(): String {
+    var sum = 0
+    for (x in xs) {
+        sum = sum * 10 + x
+        xs = IntArray(0)
+    }
+    return if (sum == 123) "OK" else "Fail: $sum"
+}