feature: initial LSP support

[tdejager]

This MR adds support for the initial LSP scaffolding and can be started from the mun main executable using:

mun language-server

Note that currently only diagnostics are supported, but it is a nice starting point for future developments. The README now contains instructions on how to use this in either vscode or vim.

[Wodann]

Very nice work! Happy to see the Mun language server coming together 👏

[Wodann]

Thanks for incorporating some of the fixes. It'd be good to merge this sooner rather than later, but there are still several outstanding questions.

The commit history is also a bit of a mess, which is fine during the review process but not once we merge. More details are outlined in our contributing guidelines.

[codecov]

Codecov Report

Merging #236 into master will decrease coverage by 2.15%.
The diff coverage is 23.00%.

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
- Coverage   81.10%   78.94%   -2.16%     
==========================================
  Files         189      196       +7     
  Lines       12325    12608     +283     
==========================================
- Hits         9996     9954      -42     
- Misses       2329     2654     +325     

Impacted Files	Coverage Δ
crates/mun_compiler/src/driver/display_color.rs	71.42% <ø> (ø)
crates/mun_compiler_daemon/src/lib.rs	0.00% <0.00%> (ø)
crates/mun_hir/src/db.rs	100.00% <ø> (ø)
crates/mun_language_server/src/cancelation.rs	0.00% <0.00%> (ø)
crates/mun_language_server/src/capabilities.rs	0.00% <0.00%> (ø)
crates/mun_language_server/src/conversion.rs	0.00% <0.00%> (ø)
crates/mun_language_server/src/diagnostics.rs	0.00% <0.00%> (ø)
crates/mun_language_server/src/lib.rs	0.00% <0.00%> (ø)
crates/mun_language_server/src/protocol/message.rs	18.82% <ø> (ø)
crates/mun_syntax/src/lib.rs	69.56% <ø> (-2.18%)	⬇️
... and 67 more

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