* lisp/emacs-lisp/rmc.el (rmc--add-key-description): Factor out
new function from...
(read-multiple-choice): ...here.
* test/lisp/emacs-lisp/rmc-tests.el (test-rmc--add-key-description)
(test-rmc--add-key-description/with-attributes)
(test-rmc--add-key-description/non-graphical-display): New tests.
* test/lisp/emacs-lisp/rmc-tests.el (test-read-multiple-choice):
Rebind read-event, read-multiple-choice uses that since 2019-05-26
"Avoid infloop in read-multiple-choice (Bug#32257)".