feat(lsp-mojo): add LSP support for Mojo 🔥

[adamliter]

Not super familiar with elisp or the lsp-mode code base, but here is an attempt to add support for Mojo 🔥 (closes #4206). Very much open to feedback on this PR! 😄 Do I need to do anything to update the documentation or anything? I think I saw somewhere that the docs are autogenerated.

Also, let me know if there's any testing that should be added to this PR (would appreciate a pointer in how to do that). I've tested this out locally by doing the following, and it seems to be working for me.

cd /tmp
git clone https://github.com/modularml/mojo.git
cat << EOF > init.el
(defvar bootstrap-version)
(let ((bootstrap-file
       (expand-file-name "straight/repos/straight.el/bootstrap.el" user-emacs-directory))
      (bootstrap-version 6))
  (unless (file-exists-p bootstrap-file)
    (with-current-buffer
        (url-retrieve-synchronously
         "https://raw.githubusercontent.com/radian-software/straight.el/develop/install.el"
         'silent 'inhibit-cookies)
      (goto-char (point-max))
      (eval-print-last-sexp)))
  (load bootstrap-file nil 'nomessage))
(straight-use-package 'use-package)
(setq straight-use-package-by-default t)

(use-package lsp-mode
  ;; my local copy of this repo with the changes in this PR
  :load-path "/Users/adamliter/git/lsp-mode" 
  :straight (:local-repo "/Users/adamliter/git/lsp-mode"))

(use-package company)
EOF
emacs -q --load init.el &

Then, I did C-x C-f mojo/examples/matmul.mojo, then M-x lsp-mode, then you can see I'm getting completion from the LSP with lsp-mode and company like so:

[yyoncho]

Thank you for contributing to lsp-mode!