POC #22510 -- Reworked opting out from a base class form fields.

Using standard inheritance shadowing to opt out from a field
turned out problematic.

When a field is called `media`, it would be automatically shadowed
because of the monkeypatching from MediaDefiningClass.

When a field has the same name as a method, overloading the method
in a subclass would shadow the field.

Ref #8620, #19617.