[eglot] Add support for eglot lsp client in emacs

- Update README
- Add eglot-specifics to cc, rs, py, hs
  removing unused lsp-mode packages when eglot is active
- Add eglot-specific bindings
- Add doctor warnings for debugger +lsp and +peek
- Add eglot-backed lookup-handlers
- Add flycheck checker using eglot for :checkers
  syntax users (using flycheck/flycheck#1676 and
  flycheck/flycheck#1592 discussion).
  This implementation is based on @marsam code, and uses recent
  Flycheck development in order to make the code smaller and
  easier to maintain.

modules/lang/rust/config.el

@@ -27,6 +27,11 @@
     (after! rustic-flycheck
       (add-to-list 'flycheck-checkers 'rustic-clippy)))
 
+  (when (featurep! +lsp)
+    (if (featurep! :tools lsp +eglot)
+        (setq rustic-lsp-client 'eglot)
+      (setq rustic-lsp-client 'lsp-mode)))
+
   (map! :map rustic-mode-map
         :localleader
         (:prefix ("b" . "build")