Ability to set heading anchor link id (useful for i18n)

[slorber]

🚀 Feature

There are 2 usecases for letting user choose its own anchor ids instead of generating them from text.

The i18n process. If a translator translate the heading of a doc, the auto generated ids will change, which means that incoming anchor links from all the other places will break, and this can be annoying. See also the section on i18n RFC: #3317

Related links:
reactjs/react.dev#1605 (comment)
reactjs/react.dev#1605 (comment)
ethereum/ethereum-org-website#272
https://github.com/reactjs/reactjs.org/pull/1636/files
mdx-js/mdx#810

Unfortunately there's no special syntax in MD/MDX that allows to pass additional metadata to headings that we could use to generate anchor links

We should probably create a remark plugin that enables us to set explicit ids to each heading, so that they become "stable".

Also related to the ability to detect broken anchor links: #3321

[slorber]

Note: the problem of broken anchors affect Docusaurus v1 as well.

For example https://jestjs.io/docs/ja/configuration#snapshotserializers-arraystring

It links to https://jestjs.io/docs/ja/tutorial-react-native#snapshot-test

But #snapshot-test id does not exist.

The anchor got translated.

https://jestjs.io/docs/ja/tutorial-react-native#%E3%82%B9%E3%83%8A%E3%83%83%E3%83%97%E3%82%B7%E3%83%A7%E3%83%83%E3%83%88%E3%83%86%E3%82%B9%E3%83%88