Eglot: allow customizing the mode line (bug#71823)

Eglot: allow customizing the mode line (bug#71823)

* lisp/progmodes/eglot.el (eglot-code-action-indications): Adjust docstring.
(eglot--mode-line-props): Tweak.
(eglot--mode-line-format): Delete.
(eglot-mode-line-format): New defcustom.
(eglot-mode-line-menu, eglot-mode-line-session)
(eglot-mode-line-error, eglot-mode-line-pending-requests)
(eglot-mode-line-progress, eglot-mode-line-action-suggestion): New
constants.
(mode-line-misc-info): Adjust setting

* etc/EGLOT-NEWS: Mention new feature.

* doc/misc/eglot.texi (Customization Variables): Mention new variable.

(cherry picked from commit b4e9115f4fcfc174a9c3b974bf414ae4af060ae7)