Eglot: suggest code actions at point

Eglot: suggest code actions at point

* lisp/progmodes/eglot.el (eglot-code-action-indicator-face): New face.
(eglot-code-action-indications, eglot-code-action-indicator): New defcustoms.
(eglot--highlights): Move up here.
(eglot--managed-mode): Rework.
(eglot--server-menu-map, eglot--main-menu-map): Extract maps into
variables (avoids odd mode-line bug).
(eglot--mode-line-format): Rework.
(eglot--code-action-params): New helper.
(eglot-code-actions): Rework.
(eglot--read-execute-code-action): Tweak.
(eglot-code-action-suggestion): New function.

* etc/EGLOT-NEWS: Mention new feature.

* doc/misc/eglot.texi (Eglot Features): Mention new feature.
(Customization Variables): Mention new variables.

(cherry picked from commit d6a502fc7a69dfa11aa100da5966a6962a82f613)