JS backend: compile primitive iterators from builtins as part of stdlib.

js/js.translator/testData/inheritance/cases/inheritFromCharIterator.kt

@@ -0,0 +1,19 @@
+package foo
+
+class MyCharIterator : CharIterator() {
+    val data = array('O', 'K')
+    var i = 0
+
+    override fun hasNext(): Boolean = i < data.size
+    override fun nextChar(): Char = data[i++]
+}
+
+fun box(): String {
+    var r = ""
+
+    for (v in MyCharIterator()) {
+        r += v
+    }
+
+    return r
+}