feat: allow multiple language servers for a hover event

[rotmh]

This is a draft for previewing hover responses from multiple language server. For example, with two language servers (taplo and harper-ls), this will be presented on hover:

taplo

This is the rust edition, valid options are...

---

harper-ls

Did you mean to spell `didnt` this way?

Instead of this (what is currently shown):

This is the rust edition, valid options are...

Currently, helix will choose the first language server that supports hover, and only work with it.

I wanted this feature, as I was working with multiple language servers, that both provide hover. Also, I saw a TODO in the hover function that suggests that this is something we want:

helix/helix-term/src/commands/lsp.rs

Line 1014 in aac0ce5

// TODO support multiple language servers (merge UI somehow)

This is my first PR, so please point my attention if I missed something.

[the-mikedavis]

I've just merged #10122 which adds the UI for hover with multiple language servers so this can be closed out. Note that the UI is a bit different #9744 is similar to this change but in #10122 each hover response is cycled through with A-n/A-p

[rotmh]

Oh, cool! Sorry for not noticing that PR...