Optimize latency when unlocking phone

Latency when unlocking the phone regressed a bit for two reasons:
- For lockscreen -> app we now have to create a full starting
window containing the snapshot, while previously this was just
showing a surface.
- For lockscreen -> home, we can't use the saved surface anymore
because currently we don't support snapshotting translucent
activities. However, in the long term, we want home screen to be
more involved into transitions anyways, so we'll have to wait for
the first frame draw anyways.

However, crystal ball trainee developer Jorim added some
artificial latency in this transition 3 years ago, because he knew
that it is going to be an issue at some point so we have some
headroom to improve! Genius! On a more serious note, it was because
he didn't understand how to read systraces with binders involved (to
be fair, there was also no binder tracing).

Now, we can completely fix the introduces latencies above by
removing this latency of 100ms, and we are 30-70ms better than
before! However, this requires a lot of discipline in SystemUI.
Currently, the callback to dismiss Keyguard takes around 30ms. By
moving all non-essential binder calls of the main thread or to the
next frame, we bring this down to 5ms, such that window animation
and Keyguard animation starts about at the same time.

Test: Take systrace, unlock phone...profit!

Fixes: 38294347
Change-Id: I481fe4ecf358ed09f7142dd9e7ecd290b53c500c
Merged-In: I3ea672bc2eca47221bc6c9f3d7c56b6899df207d