Search and highlight symbol at point.

Search and highlight symbol at point.

* doc/emacs/display.texi (Highlight Interactively): Add global keybindings
with the key prefix `M-s h'.  Document old command `highlight-phrase'.
Document new command `highlight-symbol-at-point'.

* lisp/bindings.el (search-map): Bind `highlight-symbol-at-point' to
`M-s h .'.

* lisp/hi-lock.el (highlight-symbol-at-point): New alias for the new
command `hi-lock-face-symbol-at-point'.
(hi-lock-face-symbol-at-point): New command.
(hi-lock-map): Bind `highlight-symbol-at-point' to `C-x w .'.
(hi-lock-menu): Add `highlight-symbol-at-point'.
(hi-lock-mode): Doc fix.

* lisp/isearch.el (isearch-forward-symbol-at-point): New command.
(search-map): Bind `isearch-forward-symbol-at-point' to `M-s .'.
(isearch-highlight-regexp): Add a regexp which matches
words/symbols for word/symbol mode.

* lisp/subr.el (find-tag-default-bounds): New function with the body
mostly moved from `find-tag-default'.
(find-tag-default): Move most code to `find-tag-default-bounds',
call it and apply `buffer-substring-no-properties' afterwards.

Fixes: debbugs:14427