feat: adds lsp document symbol provider

[baszalmstra]

Adds an LSP document symbol provider. The result is based on the AST of a SourceFile. The implementation is adapted from the rust-analyzer code.

[codecov]

Codecov Report

Merging #293 (3a0bdaa) into master (30bfe19) will increase coverage by 1.31%.
The diff coverage is 83.79%.

@@            Coverage Diff             @@
##           master     #293      +/-   ##
==========================================
+ Coverage   79.51%   80.83%   +1.31%     
==========================================
  Files         228      230       +2     
  Lines       13425    13587     +162     
==========================================
+ Hits        10675    10983     +308     
+ Misses       2750     2604     -146     

Impacted Files	Coverage Δ
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/lib.rs	0.00% <0.00%> (ø)
crates/mun_syntax/src/lib.rs	63.04% <ø> (ø)
crates/mun_language_server/src/main_loop.rs	64.04% <73.84%> (+40.23%)	⬆️
crates/mun_language_server/tests/support.rs	83.11% <86.48%> (+1.48%)	⬆️
crates/mun_language_server/src/analysis.rs	100.00% <100.00%> (+75.00%)	⬆️
crates/mun_language_server/src/conversion.rs	60.00% <100.00%> (+60.00%)	⬆️
crates/mun_language_server/src/file_structure.rs	100.00% <100.00%> (ø)
...tes/mun_language_server/src/protocol/connection.rs	31.25% <100.00%> (+2.08%)	⬆️
... and 16 more

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[baszalmstra]

Im gonna write some tests. Dont merge yet ;)

[baszalmstra]

I ran into a bunch of issues with the VFS. These things have been fixed in #294 . I will rebase this PR on that one.

[baszalmstra]

This has been superseded by #297