Make Array.indices extension property, move to stdlib

This is not something that needs to be intrinsified. Note that compiler
optimizations are still possible and the fact whether 'indices' is a member or
an extension is irrelevant to the optimizer

js/js.translator/testData/kotlin_lib.js

@@ -974,10 +974,6 @@
         return result;
     };
 
-    Kotlin.arrayIndices = function (arr) {
-        return new Kotlin.NumberRange(0, arr.length - 1);
-    };
-
     Kotlin.arrayIterator = function (array) {
         return new Kotlin.ArrayIterator(array);
     };