SF: Commit initial DisplayState under lock

The main thread must `applyTransactions` under `mStateLock` during
`onInitializeDisplays`, since a Binder thread could be concurrently
writing to `mCurrentState.displays` while creating or destroying a
virtual display.

Fixes: 244460929
Test: Boot (sporadic crash with no repro steps)
Change-Id: I4f8bac4af7635b9b93c7b79826285a26a109cf9e