resourceloader: Merge 'user.groups' into 'user' module
This is with T92459 in mind to simplify the process of splitting
the 'user' module for the styles-only queue.
Consequences:
* Cached HTML isn't relevant in practice since there is no caching for logged-in
users and this module is only for logged-in users. Even then, cached HTML will
work and may happen as browsers re-use HTML responses when revisiting a
privately cached page (after 304 Not Modified).
Note that OutputPage (via isKnownEmpty) only actually tries to load 'user.groups'
if the wiki has 'MediaWiki:Group-*.{js,css}' pages for the current user's groups.
- Old style queue request will continue to ask for user.groups which is now a
FileModule with no styles (simply concats the empty string to the bundle)
- Old load() request will resolve with an empty function.
* The are no known dependants of 'user.groups'. If there are, they will work
by proxy of it now being an empty module that just ensures 'user' is loaded.
* The security origin of 'user.groups' was USER_SITEWIDE. The origin of 'user'
is lower (USER_INDIVIDUAL). Pages that are restricted to USER_SITEWIDE
previously received user.groups, but won't anymore. This should be fine as
OutputPage::reduceAllowedModules() is mainly used to either allow everything
or restrict all the way down to CORE. The only exception is disallowUserJs()
if $wgAllowSiteCSSOnRestrictedPages is enabled (T73621) but that edge case was
made for Common.css, not Group-*.css.
Change-Id: I74cd2368ebd2989c5e1c22bea491a80beb0319dc