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

compiler/testData/codegen/box/vararg/kt581.kt

@@ -3,7 +3,7 @@ package whats.the.difference
 import java.util.HashSet
 
 fun iarray(vararg a : Int) = a // BUG
-
+val IntArray.indices: IntRange get() = IntRange(0, lastIndex())
 fun IntArray.lastIndex() = size() - 1
 
 fun box() : String {