scripts/documentation-file-ref-check: rewrite it in perl with auto-fix mode

The original shell script works, but:
	1) it is too slow;
	2) it is hard to exclude rejex patterns

Convert it to perl.

Here, the new version is able to check the entire tree in
less than a second (after cached):

	real	0m0,284s
	user	0m0,668s
	sys	0m0,778s

The old version takes more than a minute to complete (also
after cached):
	real	1m17,905s
	user	0m25,583s
	sys	0m55,334s

It also produce less false-positives (if any).

The new script also contains an auto-fix mode.

Usually, file references get lost when they're moved to some other
place and/or renamed to .rst.

Add an experimental mode to auto-fix those.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>