Turn typing.List, typing.Dict, etc into simple aliases of list, dict, etc

[tmke8]

The recent proposal in python-ideas to rename classes in the standard library to have CamelCase names, reminded me that list, dict, tuple, set, frozenset already have CamelCase aliases in the typing module. However, they can't be used to instantiate anything:

>>> List(2*x for x in range(3))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/tmk/.conda/envs/palbolts/lib/python3.9/typing.py", line 675, in __call__
    raise TypeError(f"Type {self._name} cannot be instantiated; "
TypeError: Type List cannot be instantiated; use list() instead

But with PEP 585, there is no real reason to keep builtins.list distinct from typing.List, right? The CamelCase aliases in the typing module could just stay there indefinitely for people who want their classes to be in CamelCase.

You could maybe argue that this situation would be confusing to newcomers, but code from the era 3.6-3.8 is already littered with typing.List, typing.Dict, etc so it doesn't really make the situation worse.

There was discussion about this #367 where it was concluded that List[int]() should not be allowed, but that point is now kind of moot because since PEP 585, list[int]() is already allowed, so I don't see a good reason why List[int]() would be worse.

[sobolevn]

Important note: they are different right now:

>>> list[1]
list[1]
>>> from typing import List
>>> List[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/sobolev/.pyenv/versions/3.9.1/lib/python3.9/typing.py", line 262, in inner
    return func(*args, **kwds)
  File "/Users/sobolev/.pyenv/versions/3.9.1/lib/python3.9/typing.py", line 814, in __getitem__
    params = tuple(_type_check(p, msg) for p in params)
  File "/Users/sobolev/.pyenv/versions/3.9.1/lib/python3.9/typing.py", line 814, in <genexpr>
    params = tuple(_type_check(p, msg) for p in params)
  File "/Users/sobolev/.pyenv/versions/3.9.1/lib/python3.9/typing.py", line 151, in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
TypeError: Parameters to generic types must be types. Got 1.

[JelleZijlstra]

I'd rather not do this. The point of typing.py isn't to help "people who want their classes to be in CamelCase", it's to provide helpers for type annotating your code. The camel case aliases are still there for compatibility but should eventually be removed.