lang/julia: improve lsp support (#4012)

* lang/julia: include lsp-julia w/o language server

Use nonrecursive clone to get lsp-julia without bundled
LanguageServer.jl (plus dependencies) and include instructions in the
README on how to install the language server (bundled or otherwise).

* lang/julia: add checks for julia +lsp in doctor

Add two checks, both only for when the +lsp feature is enabled:
- Check if (:tools lsp) is selected
- Check if LanguageServer.jl is installed

* lang/julia: indicate SymbolServer.jl as dependency

It is itself a dependency of LanguageServer.jl, but it's necessary to
add it separately in order to do `using SymbolServer`.

* tools/lsp: add julia language server to list

* lang/julia: add eglot support using eglot-jl

Forcing eglot-jl to not install its own LanguageServer.jl is a bit of a
hack though.

* lang/julia: make timeout increase buffer-local

Suggestion by @benneti to use `setq-local` instead of `setq` to prevent
a timeout increase in non-Julia eglot buffers.

* Fix issues

Co-authored-by: Henrik Lissner <henrik@lissner.net>

docs/modules.org

@@ -118,7 +118,7 @@ Modules that bring support for a language or group of languages to Emacs.
 + java =+meghanada +eclim +lsp= - TODO
 + [[file:../modules/lang/javascript/README.org][javascript]] =+lsp= - JavaScript, TypeScript, and CoffeeScript support
 + [[file:../modules/lang/json/README.org][json]] =+lsp= - TODO
-+ julia =+lsp= - TODO
++ [[file:../modules/lang/julia/README.org][julia]] =+lsp= - TODO
 + kotlin =+lsp+= - TODO
 + [[file:../modules/lang/latex/README.org][latex]] =+latexmk +cdlatex +fold +lsp= - TODO
 + lean - TODO