Don't merge conditional FuncDef
after an unconditional one.

Allow subclasses to override `__match_args__` freely, and don't require
`__match_args__` to be final. 

This matches runtime behavior. For example, if `B` subclasses `A`, 
`case A(...)` also matches instances of `B`, using the `__match_args__` 
from `A`.

The issue was brough up by @AlexWaygood in 
#12411 (comment).

Fixes #12416.

Allows any dunder (`__name__`) attributes except `__members__` (due to it being 
read-only) to be overridden in enum subclasses.

Fixes #12132.

Multiple inheritance from dataclasses and attrs classes works at runtime,
so don't complain about `__match_args__` or `__attrs_attrs__` which tend
to have incompatible types in subclasses.

Fixes #12349. Fixes #12008. Fixes #12065.

Various things can go wrong if the order of modules in the builtins
SCC that also includes typing, _typeshed and others is adjusted.

Hopefully fixes #12422. May also fix #12421.

A wider return type can be useful if a decorator used for the overload
implementation gets a more precise return type as part of a typeshed
update.

Closes #12434.