Move kernel baseline tests to front_end.

pkg/front_end/testcases/null_aware.dart.outline.expect

 library;
 import self as self;
 import "dart:core" as core;
 
 class Foo extends core::Object {
+  field core::int field;
+  static field core::int staticField;
   constructor •() → void
     ;
 }
-class Bar extends self::Foo {
-  static factory •() → self::Bar
-    ;
-}
 static method main() → dynamic
   ;