Single source revcheck code/data (#174)

Rewrite of `doc-base`'s `revcheck.php`, removing code duplication.

* DTO for revcheck data.
* Preparation for revcheck data exporting.
* Backport loose and fixed [skip-revcheck] modes
* Additional revcheck data.
* Revcheck deduplication: clean up, header.
* Revcheck deduplication: translators, file summary.
* Revcheck deduplication: old/wip files.
* Move backport code and docs to a separate file.
* Revcheck deduplication: backport couting behaviour.
* Revcheck deduplication: more backport couting woes.
* Revcheck deduplication: notinen, revtag, unstranslated.
* Revcheck deduplication: ignore, regex, xml.
* Revcheck deduplication: adds/dels, clean up.
* Revcheck deduplicatoin: genrevdb.php.
* Revcheck deduplicatoin: genrevdb.php.
* More backport and small fixes.
* Review changes/fixes.
* Better log messages.
* Remove unrelated filter.
---------
Co-authored-by: André L F S Bacci <ae@php.net>

.gitignore

@@ -1,5 +1,6 @@
 # Files generated by the configure script
 .manual.xml
+.revcheck.json
 install-unix.xml
 install-win.xml
 manual.xml