[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/tools/lsp/autoload/eglot.el

@@ -0,0 +1,19 @@
+;;; tools/lsp/autoload/eglot.el -*- lexical-binding: t; -*-
+;;;###if (featurep! +eglot)
+
+;;;###autodef
+(defun set-eglot-client! (mode server-call)
+  "Add SERVER-CALL list as a possible lsp server for given major MODE.
+
+Example : (set-eglot-client! 'python-mode `(,(concat doom-etc-dir \"lsp/mspyls/Microsoft.Python.LanguageServer\")))"
+  (when (featurep! +eglot)
+    (add-to-list 'eglot-server-programs `(,mode . ,server-call))))
+
+;;;###autoload
+(defun +eglot/documentation-lookup-handler ()
+  "Documentation lookup handler using eglot :document/hover handler.
+
+Mostly a rewrite of `eglot-help-at-point', which should be used interactively."
+  (interactive)
+  (eglot-help-at-point)
+  (display-buffer eglot--help-buffer))