Convert member to extension: Support members of header/impl classes

#KT-18883 Fixed

idea/testData/multiModuleQuickFix/memberFunToExtensionByHeader/js/js.kt

@@ -0,0 +1,5 @@
+impl class Foo {
+    impl fun foo(n: Int) {
+
+    }
+}

idea/testData/multiModuleQuickFix/memberFunToExtensionByHeader/js/js.kt.after

@@ -0,0 +1,6 @@
+impl class Foo {
+}
+
+impl fun Foo.foo(n: Int) {
+
+}