[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/cc/packages.el

@@ -17,7 +17,9 @@
       :pin "404cd0694a")))
 
 (if (featurep! +lsp)
-    (package! ccls :pin "17ec7bb4cf")
+    (unless (featurep! :tools lsp +eglot)
+      ;; ccls package is necessary only for lsp-mode.
+      (package! ccls :pin "17ec7bb4cf"))
   (when (package! irony :pin "5f75fc0c92")
     (package! irony-eldoc :pin "0df5831eaa")
     (when (featurep! :checkers syntax)