Link from typing docs to specific sections in the typing spec

The typing docs currently frequently link to the PEPs that defined new typing features. Instead, they should link to the typing spec, which unlike the PEPs is a living document.

In the online documentation, we can do this with intersphinx. I have this running locally and can send a PR.

I'm less sure about how to handle this in the docstrings. For example, Protocol's docstring refers to PEP 544: https://github.com/python/cpython/blob/b32789ccb91bbe43e88193f68b1364a8da6d9866/Lib/typing.py#L1987. Should we provide a full URL to the spec, like https://typing.readthedocs.io/en/latest/spec/protocol.html?

Linked PRs

• gh-117540

首先检查 typing 文档链接和 intersphinx 配置，然后查看 Lib/typing.py 中所引用的 PEP 544 链接附近的 Protocol 文档字符串。确定在线文档和文档字符串应如何指向现行的 typing 规范，并验证相关链接使用了规范中预期的章节。