Rename or remove addMarkdownHighlighter

[Snapstromegon]

Is your feature request related to a problem? Please describe.

In general the add*() functions of the eleventy config are non-destructive if possible. addMarkdownHightlighter() on the other hand behaves like the set*() functions.

Also this function IMO is no longer necessary, since there are other, better and better documented options in eleventy.

Function in code:
https://github.com/11ty/eleventy/blob/main/src/UserConfig.js#L170

Describe the solution you'd like

I would recommend to either remove this function completely with the next major version, or to rename it to setMarkdownHighlighter() and add documentation for it.

Describe alternatives you've considered

Not changing anything is possible, but leaves this in a weird state.

Additional context

No response