Make Array.size() a function instead of a property

Also add a deprecated extension property to help migration. This is done to
unify getting size of arrays and collections

compiler/testData/codegen/box/functions/kt3214.kt

@@ -1,9 +1,9 @@
 class A {
-    fun get(vararg x: Int) = x.size
+    fun get(vararg x: Int) = x.size()
 }
 
 class B {
-    fun get(vararg x: Unit) = x.size
+    fun get(vararg x: Unit) = x.size()
 }
 
 fun test1(a: A): Int {