List generic arguments for `collections.abc` base classes in documentation

Documentation

When #123544 lands, we'll have PEP585-related documentation spread even further than before. Deprecated aliases in typing correctly list the generic arguments, but are otherwise undocumented - all such entries boil down to "deprecated in favour of collections.abc.X".

Several relevant changes were discussed along #123523.

There's no direct way for a user to find generic parameters of collections.abc.Generator - they are listed for typing.Generator and in "annotating generators and coroutines" section in typing docs (the latter linked from collections.abc.Generator, though).

I'm certain that generic arguments represent an essential part of class' "signature" - basic amount of information we need to see to use it somehow.

However, collections.abc is not really a type-hinting module, hence providing those signatures there directly can add too much cognitive load.

As of now, my best suggestion is to introduce "Type parameters" section for each generic alias there, like this:

.. class:: Mapping
           MutableMapping

   ABCs for read-only and mutable :term:`mappings <mapping>`.

   Type arguments:

   * ``Mapping[KT, VT_co](Collection[KT])``
   * ``MutableMapping[KT, VT](Mapping[KT, VT])``

cc @AA-Turner and @AlexWaygood - we started this discussion in the PR above.

先檢閱現有的 collections.abc 文件、已棄用 typing 別名的泛型引數列表，以及 #123544 和 #123523 中的相關討論。為相關的泛型別名新增一致的 Type parameters 區段，列出其引數和關係，並確認使用者可以從 collections.abc 項目中找到這些資訊。