[code-transform] Generate non-existing constants / properties

[dantleech]

As with the existing generate non-existing method regactoring, allow the same with all other class members:

class Foo
{
}

$foo = new Foo();
$foo->b<>ar;

should add the property bar to Foo.

[mamazu]

This should work now. At least you can use that from inside the class.