fix(lsp): eglot-ensure advice nooping in some major modes

Due to the nested structure of eglot-server-programs, our advice would
not correctly detect entries for some modes (like javascript modes),
effectively disabling Eglot in those modes.

I've replaced the advice with a solution baked into lsp!, so folks still
have the option of using eglot-ensure directly if they want it activated
unconditionally.

Amend: #7219

modules/tools/lsp/autoload/common.el

@@ -5,6 +5,9 @@
   "Dispatch to call the currently used lsp client entrypoint"
   (interactive)
   (if (modulep! +eglot)
-      (eglot-ensure)
+      (when (require 'eglot nil t)
+        (if (eglot--lookup-mode major-mode)
+            (eglot-ensure)
+          (eglot--message "No client defined for %s" major-mode)))
     (unless (bound-and-true-p lsp-mode)
       (lsp-deferred))))