* The button's icon was missing because at some point in the
past two years, the CSS for this was moved out of the
main theme CSS files and into its own 'images' theme file,
which was not yet loaded.
Fix this by adding a <link> element, and also add the file
to the whitelist as it was previously also not comitted to
the repo (because for MW, RL creates this directly based
on the JSON).
This aligns closer to VE's /lib/oojs-ui directory.
* Also fix the "require() undefined" warning, although it
didn't break the demo below it, it is noise.
This is because mediawiki.base was converted to a packageFiles
module recently and it now assumes a require() function exists,
similar to what startup/mediawiki.js would provide during
debug mode. Mock that as well for consistency.
Bug: T168812
Change-Id: Ide9ef38c38782515becdae5fc40eac4ee9b384fc
567001e169