New transient mode 'repeat-mode' to allow shorter key sequences (bug#46515)

New transient mode 'repeat-mode' to allow shorter key sequences (bug#46515)

* doc/emacs/basic.texi (Repeating): Document repeat-mode.

* lisp/repeat.el (repeat-exit-key): New defcustom.
(repeat-mode): New global minor mode.
(repeat-post-hook): New function.

* lisp/bindings.el (undo-repeat-map): New variable.
(undo): Put 'repeat-map' property with
'undo-repeat-map'.
(next-error-repeat-map): New variable.
(next-error, previous-error): Put 'repeat-map' property with
'next-error-repeat-map'.

* lisp/window.el (other-window-repeat-map): New variable.
(other-window): Put 'repeat-map' property with
'other-window-repeat-map'.
(resize-window-repeat-map): New variable.
(enlarge-window, enlarge-window-horizontally)
(shrink-window-horizontally, shrink-window): Put 'repeat-map'
property with 'resize-window-repeat-map'.