Offer Mainline stubs under Ravenwood.

Mainline hidden APIs can change at any time, so we don't want to
bring them across as-is, so `all-updatable-modules-system-stubs`
is used instead to ensure we only bring across published stub APIs
that module authors intend to be stable.

Bug: 319647875
Test: atest SystemUiRavenTests
Change-Id: Ib0837ee65ce125f27e0e7f3da6effe814065c35b