[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/config.el

@@ -236,9 +236,45 @@ If rtags or rdm aren't available, fail silently instead of throwing a breaking e
       (setq-local company-lsp-cache-candidates nil)
       (lsp!))))
 
+(when (and (featurep! +lsp) (featurep! :tools lsp +eglot))
+  ;; TODO : test this value
+  ;; IS-MAC custom configuration
+  (when IS-MAC
+    (add-to-list 'eglot-workspace-configuration
+                 ((:ccls . ((:clang . ,(list :extraArgs ["-isystem/Library/Developer/CommandLineTools/usr/include/c++/v1"
+                                      "-isystem/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include"
+                                      "-isystem/usr/local/include"]
+                          :resourceDir (string-trim (shell-command-to-string "clang -print-resource-dir")))))))))
+  ;; Eglot specific helper, courtesy of MaskRay
+  (defun eglot-ccls-inheritance-hierarchy (&optional derived)
+  "Show inheritance hierarchy for the thing at point.
+If DERIVED is non-nil (interactively, with prefix argument), show
+the children of class at point."
+  (interactive "P")
+  (if-let* ((res (jsonrpc-request
+                  (eglot--current-server-or-lose)
+                  :$ccls/inheritance
+                  (append (eglot--TextDocumentPositionParams)
+                          `(:derived ,(if derived t :json-false))
+                          '(:levels 100) '(:hierarchy t))))
+            (tree (list (cons 0 res))))
+      (with-help-window "*ccls inheritance*"
+        (with-current-buffer standard-output
+          (while tree
+            (pcase-let ((`(,depth . ,node) (pop tree)))
+              (cl-destructuring-bind (&key uri range) (plist-get node :location)
+                (insert (make-string depth ?\ ) (plist-get node :name) "\n")
+                (make-text-button (+ (point-at-bol 0) depth) (point-at-eol 0)
+                                  'action (lambda (_arg)
+                                            (interactive)
+                                            (find-file (eglot--uri-to-path uri))
+                                            (goto-char (car (eglot--range-region range)))))
+                (cl-loop for child across (plist-get node :children)
+                         do (push (cons (1+ depth) child) tree)))))))
+    (eglot--error "Hierarchy unavailable"))))
 
 (use-package! ccls
-  :when (featurep! +lsp)
+  :when (and (featurep! +lsp) (not (featurep! :tools lsp +eglot)))
   :after lsp
   :init
   (after! projectile