Julia LanguageServer: improve startup time

[thomasjm]

Doing some profiling, it seems that the call to run(server) takes about 10 seconds before it actually starts running the code in the Base.run override for LanguageServerInstance. Is it precompiling?

[thomasjm]

https://julialang.slack.com/archives/C013J5F9USH/p1682472242561679

https://discourse.julialang.org/t/precompiling-languageserver-runserver-with-precompiletools-jl/97926

[thomasjm]

This was actually merged:

julia-vscode/LanguageServer.jl#1218

See if it still needs to be improved

[thomasjm]

julia-vscode/SymbolServer.jl#269