The ext.cite.referencePreviews module will transparently replace the
ext.popups.referencePreviews module after this patch. Configuration
stays in Popups for now, we can migrate it in later work.
CSS classes may be renamed in the future but this will be handled
separately since it could be a breaking change for on-wiki
customizations.
A lot of fancy footwork happens in this patch to emulate a soft
dependency on Popups. This mechanism doesn't exist explicitly in
either ResourceLoader or QUnit, so lots of workarounds are used, to
conditionally load the module and to dynamically skip dependent tests.
renderer.test.js is fully skipped for now, but can be wired up in
later work.
Bug: T355194
Change-Id: I0dc47abb59a40d4e41e7dda0eb7b415a2e1ae508
