mediawiki.special.recentchanges: Use module.exports instead of mw.special

mediawiki.special.recentchanges: Use module.exports instead of mw.special

This isn't generally used as a public method. The only reason it's exposed is
for an integration test to access it.

This commit and others prepare for removal of the 'mediawiki.special.js' file.
This script does nothing other than create "mw.special = {};". While that init
pattern is common in extensions and not wrong, 'mediawiki.special' violates
T92459 due to having styles. Given there's only script uses of it, it's easiest
to remove it in favour of the new module export pattern.

Change-Id: I2e78828828601e1160550efe02c07172ac32e985