Improve repeat-continue property handling

Improve repeat-continue property handling

* lisp/repeat.el (repeat-get-map-sym): Support 'repeat-continue'
property value of t to continue any active repeat map (suggested
by Karthik Chikmagalur <karthikchikmagalur@gmail.com>).
Simplify logic so that repeat-continue does not interfere with
repeat-map activation.
(repeat-check-map): Allow commands with 'repeat-continue'
property value of t to continue without checking the key.
(repeat-mode): Update and tweak docstring.
* lisp/bind-key.el (bind-keys-form): Update handling of
':continue-only' keyword: only add keymap to 'repeat-continue'
if current value is a list.
(bind-keys): Update documentation, mirroring bind-keys-form.
* lisp/keymap.el (defvar-keymap): Update handling of ':continue'
keyword: only add keymap to 'repeat-continue' if current value
is a list.
* test/lisp/repeat-tests.el (repeat-tests-continue)
(repeat-tests-continue-another): Enable previously commented
tests that now work correctly.
* etc/NEWS: Update announcement of 'repeat-continue' (bug#78742).

(cherry picked from commit 3a0def802cf576902faafde404d15f079786a2f8)