Add new keyword :continue-only to defvar-keymap for repeat-mode (bug#74140)

Add new keyword :continue-only to defvar-keymap for repeat-mode (bug#74140)

* doc/lispref/keymaps.texi (Creating Keymaps): Add :continue-only
to :repeat part of defvar-keymap.

* lisp/keymap.el (defvar-keymap): Add support for new :repeat
keyword :continue-only.

* lisp/repeat.el (repeat-post-hook): The property 'repeat-continue-only'
is handled as a list of repeat-maps.

* test/lisp/repeat-tests.el (repeat-tests-repeat-map): Use new
:repeat keyword :continue-only.

(cherry picked from commit 69e1f787528eaf2f223c53a6ff518ba4f984bc17)