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/config.el

@@ -65,10 +65,26 @@
     (term-set-escape-char ?\C-c)))
 
 
+(when (featurep! +lsp)
+  (add-hook 'julia-mode-local-vars-hook #'lsp!))
+
+
 (use-package! lsp-julia
   :when (featurep! +lsp)
+  :unless (featurep! :tools lsp +eglot)
   :after lsp-mode
   :preface
-  (setq lsp-julia-default-environment "~/.julia/environments/v1.0")
-  (when (featurep! +lsp)
-    (add-hook 'julia-mode-local-vars-hook #'lsp!)))
+  (setq lsp-julia-default-environment "~/.julia/environments/v1.0"))
+
+
+(use-package! eglot-jl
+  :when (featurep! +lsp)
+  :when (featurep! :tools lsp +eglot)
+  :after eglot
+  :preface
+  ;; Prevent auto-install of LanguageServer.jl
+  (setq eglot-jl-language-server-project "~/.julia/environments/v1.0")
+  :init
+  ;; Prevent timeout while installing LanguageServer.jl
+  (setq-hook! 'julia-mode-hook eglot-connect-timeout (max eglot-connect-timeout 60))
+  :config (eglot-jl-init))