[Central Surfaces] NSSLC uses BouncerInteractor for bouncer showing.

Removes a CentralSurfaces reference by asking
PrimaryBouncerInteractor directly for the status.

Note: Based on logs, once the user has successfully dismissed the
bouncer, `PrimaryBouncerInteractor#isBouncerShowing` updates
to false ~10-200ms before `CentralSurfaces#isBouncerShowing` updates to false.
However, I don't see any regressions with b/267060171 after making
this change. The change is protected by a flag in case we do notice
regerssions on other devices.

Bug: 277762009
Flag: USE_REPOS_FOR_BOUNCER_SHOWING

Test: manual: on tablet, pull up bouncer from dreaming and verify "No
new notifications" is not showing behind bouncer (aka, verify
b/267060171 has not regressed). Once PIN is successfully entered, verify
"No new notifications" is not showing during the transition either.
Test: atest NotificationStackScrollLayoutControllerTest

Change-Id: I05874ca2a770642f7e3d868eeaa3638b5fe630ee