Do not allow TypedDict classes with extra keywords

[sobolevn]

I think that sometimes metaclass= can still be used in real code, when people write compatibility layers with other metaclasses. I think that I've seen this a couple of times, but I cannot remember where and why.

In this case, this error can be precisely silenced.

[AlexWaygood]

LGTM

[sobolevn]

I realized that I want to reuse existing messages:

» mypy -c 'class A(a=1, b=2): ...'
<string>:1: error: Unexpected keyword argument "a" for "__init_subclass__" of "object"  [call-arg]
<string>:1: error: Unexpected keyword argument "b" for "__init_subclass__" of "object"  [call-arg]
Found 2 errors in 1 file (checked 1 source file)

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅