Add more language ID recommendations #2269

I noticed that the LSP specification keeps a list of recommended language IDs. I wanted to add MDX (mdx) to the list, but I suppose I best wait until there’s a new draft for LSP 3.19.

I actually noticed a larger number of language IDs I’m familiar with is missing. Should this list contain everything that’s commonly known? For example, without even looking them up in my VSCode, I see csv, dotenv, graphql, astro, svelte, vue, restructuredtext, bats, and mermaid are missing.

If LSP makes recommendations, then I think it may also be useful to recommend the use of lower case language IDs, optionally hyphenated. By far most VSCode extensions use this, but I have seen deviations.