Fix @dataclass(frozen=True) fail on name shadowing

[sobolevn]

There are two things that I've done:

1. Now we clear attributes from dataclass that are shadowed by methods. It is helpful, so __call__ won't be considered a dataclass attribute, the same as runtime does
2. assert -> if change to be safe and not fail. Why I want to be extra safe? Because we can shadow attrs with class, import, import from, @property possibly something else. I don't want to dive deep into supporting everything here, just not crashing is good enough

Feedback is welcome!

Closes #12084