PHPUnit now recognizes extension parser tests
Parser tests are registeredd by appending one or more .txt files to the
$wgParserTestFiles global setting. Since this is shared with MediaWiki
core, I have made MediaWikiParserTest a factory of PHPUnit testsuite
which would filter in/out extensions tests.
The `extensions` test suite now has a second test suite builder which is
simply a wrapper around MediaWikiParserTest factory.
Play cases:
$ php phpunit.php --group Parser --tap
Runs any parser tests including the ones coming from extensions.
With an extension having parser tests such as Cite:
$ php phpunit.php --testsuite extensions --tap
// Extensions tests are run including parser tests.
bug: 42506
Change-Id: Icc3e9d30706b32149aa9dd18552e4241ec4af67e