swiper.el (swiper-toggle-face-matching): Add and bind to "C-c C-f"
* swiper.el (swiper-map): Bind `swiper-toggle-face-matching' to
"C-c C-f".
(swiper-invocation-face): New defvar.
(swiper--ivy): Set `swiper-invocation-face'.
(swiper-toggle-face-matching): Toggle `ivy-state-matcher' between
nil (the initial value) and 'swiper--face-matcher.
(swiper--face-matcher): New defun. In addition to filtering CANDIDATES
by having them match REGEXP, also ensure that every match has
`swiper-invocation-face'.
Example of usage:
1. Move point to a variable with e.g. `font-lock-keyword-face' and "C-s"
<input>.
2. Use "C-c C-f" to filter the candidates further by selecting only the
ones that have `font-lock-keyword-face'.
Note that "M-q" (`swiper-query-replace') is also affected by the filtering.