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>

modules/lang/julia/doctor.el

@@ -0,0 +1,19 @@
+;;; lang/julia/doctor.el -*- lexical-binding: t; -*-
+
+(assert! (or (not (featurep! +lsp))
+             (featurep! :tools lsp))
+         "This module requires (:tools lsp)")
+
+(when (featurep! +lsp)
+  (let ((args
+         (cond ((require 'eglot-jl nil t)
+                `(,eglot-jl-julia-command
+                  ,(concat "--project=" eglot-jl-language-server-project)
+                  ,@eglot-jl-julia-flags
+                  "-e" "empty!(LOAD_PATH); push!(LOAD_PATH, \"@\"); using LanguageServer, SymbolServer"))
+               ((require 'lsp-julia nil t)
+                `(,lsp-julia-command
+                  ,@lsp-julia-flags
+                  "-e" "using LanguageServer, SymbolServer")))))
+    (unless (zerop (car (apply #'doom-call-process args)))
+      (warn! "Couldn't find LanguageServer.jl and/or SymbolServer.jl"))))