Revert "SECURITY: Do not show log action if revdeleted" and fix UI message

This mostly reverts commit 89b793b9f72c254f0a6142952a4239fffa8ed945. It also
finishes removing of the "fld_action" field in ApiQueryLogEvents that
was begun in that commit.

Bug: T74222
Change-Id: I185e42d029905fd2781f3ccbbef0687f51234b0d
thumb.php: Set proper output formats for messages going into HTML

* Use ->parse() instead of ->text() for wikitext messages that were
  being treated as HTML
* Explicitly specify ->parse() if no output format was set
* Document that wfThumbError() takes HTML

Bug: T76686
Change-Id: Id6e7548b2e081cfda7803772ed0395a15feb1f84
SECURITY: Fix CORS origin matching in the API

Bug: T77028
Change-Id: I68c1ee5b5a048af2aba4e710bc301b09748389bf
Updated release notes and version number to MediaWiki 1.23.8

This is MediaWiki 1.23.8 security and maintenance release.

Change-Id: I9ce82c6d4351535444b63333fbbda576fdfac5db
Merge branch 'REL1_23' of https://gerrit.wikimedia.org/r/p/mediawiki/core into REL1_23