Singletons are bad, amongst other reasons, because they're never reset
in tests. They can therefore occasionally cause test failures if the
cached data stored in one of these singletons becomes stale.
As noted on the task, ideally these two classes shouldn't exist at all,
and core should be responsible for caching the information it deems
expensive to compute.
As a temporary (TM) workaround, make both classes actual services, so
that the setUp/tearDown logic in MediaWikiIntegrationTestCase can
properly reset them between tests.
Dependencies are intentionally not being injected, precisely because
these classes should just be deleted, not improved.
Bug: T344124
Change-Id: I58b8d9610f9447468235b94d25732528ab6acce6
