feat(language server): removed async code and switched to lsp_server

[baszalmstra]

Depends on #294

This PR removes all async code and switch to the use of the lsp_server crate instead of using our own.

[codecov]

Codecov Report

Merging #295 (7119fe0) into master (044ba56) will increase coverage by 2.00%.
The diff coverage is 58.41%.

@@            Coverage Diff             @@
##           master     #295      +/-   ##
==========================================
+ Coverage   78.76%   80.77%   +2.00%     
==========================================
  Files         236      237       +1     
  Lines       13866    13864       -2     
==========================================
+ Hits        10922    11199     +277     
+ Misses       2944     2665     -279     

Impacted Files	Coverage Δ
crates/mun_language_server/src/cancelation.rs	30.00% <0.00%> (+30.00%)	⬆️
crates/mun_language_server/src/config.rs	100.00% <ø> (ø)
crates/mun_language_server/src/conversion.rs	22.22% <ø> (+22.22%)	⬆️
crates/mun_language_server/tests/initialization.rs	100.00% <ø> (ø)
crates/mun_vfs/src/monitor.rs	66.12% <0.00%> (-8.42%)	⬇️
crates/mun_language_server/src/lib.rs	6.66% <12.50%> (+6.66%)	⬆️
crates/mun_language_server/src/state/workspace.rs	73.33% <16.66%> (ø)
crates/mun_project/src/project_manifest.rs	48.14% <33.33%> (ø)
...n_language_server/src/state/protocol/dispatcher.rs	34.54% <34.54%> (ø)
crates/mun_language_server/src/state/protocol.rs	38.57% <38.57%> (ø)
... and 20 more

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[baszalmstra]

I also added some basic functionalities for testing the language server properly. This now also fixes the shortcomings in #293 where the language server was slower than the tests. With the new vfs we can now wait until the entire workspace is loaded before requesting information about it.

[Wodann]

Looks good overall. Some minor change requests.