Fix the flipping orientation lock.

We were setting ACCELEROMETER_ROTATION to 0 before putting
in the proper USER_ROTATION value, and PhoneWindowManager's
content observer would eagerly rotate the screen to the last
locked orientation before re-rotating to the updated locked
rotation.

Now we set USER_ROTATION first. Additionally, the
content observer is now the only place we set
mUserRotation{,Mode} (previously we would race with it in
setUserRotationMode()).

Bug: 3425657
Change-Id: I04ba1a3631c6d985c2e406c4d148c39fb5c36216