Inject markdown syntax for rust doc_comments

[A-Walrus]

Describe your feature request

Since rust doc comments support markdown it would be nice to highlight it as such. Especially useful for code within doc comments for which the language should be injected into the markdown which is injected into rust.

[CptPotato]

If implemented I would prefer this to be optional. Having full markdown highlighting in comments would probably distract me a lot from the actual code.

[kirawi]

tree-sitter/tree-sitter-rust#130

[the-mikedavis]

tree-sitter/tree-sitter-rust#168 looks promising for this. It works the same as #4870

[the-mikedavis]

As mentioned in #9695 this is now possible with a change to the grammar which was merged upstream. There's a bug in the highlighter though #6491 that makes injecting markdown very noisy. That should be fixed when we switch over to the new highlighter @pascalkuthe is working on (tracked in #10286) and then we should be able to enable markdown injections for rust doc comments.