Allow Services to be created through Dagger.

This is a significant change that allows Services to have their
constructed injected into.

The DozeService is now labeled as injectable (thought it takes no arguments).
At least one Service has to be marked as injectable for Dagger to be happy
compiling this code.

Bug: 138787339
Test: atest SystemUITests
Change-Id: I0ec92e01dd236bcee3083c8f8744c53b7ccc92d3
Merged-In: Ib58f8763c996fbc2aea07ead56493d2d9e936f5b