Make 'inhibit-changing-match-data' obsolete and adjust callers

Make 'inhibit-changing-match-data' obsolete and adjust callers

* doc/lispref/searching.texi (Regexp Search):
(POSIX Regexps): Document this.
* lisp/subr.el (inhibit-changing-match-data): Make obsolete.
(looking-at-p): Adjust call.

* lisp/vc/vc-hg.el (vc-hg--raw-dirstate-search):
(vc-hg--ignore-patterns-ignored-p):
(vc-hg--cached-dirstate-search): Don't use
`inhibit-changing-match-data'.

* src/minibuf.c (Ftry_completion):
(Fall_completions):
(Ftest_completion): Adjust Fstring_match calls.

* src/search.c (looking_at_1): Pass in modify_data.
(Flooking_at): Add optional inhibit-modify parameter.
(string_match_1): Pass in modify_data.
(Fstring_match):
(Fposix_looking_at, Fposix_string_match): Add optional
inhibit-modify parameter.