Fix window manager policy state when waking from doze.

Once upon a time when the world was fresh and new, the heavens
had an easy rhythm.  Day and night.  Night and day.  In the day,
the pixel fairies would cavort and play in the bright gardens
with narry a mark of shadow or gloom.  In the night, they would
rest peacefully, dreaming no dreams and knowing no fear.

Then one night a fairy dreamed the first dream.  At first
the dream was peaceful, full of colors and delight, hopes and
memories.  Then all at once, jarringly, it awoke in bright
daylight.  The pixel fairy knew fear, for the world had changed
and it was unprepared.

Time passed and the pixel fairies grew accustomed to their
fate, day and night, night and day, sometimes dreaming, until
there came a night when a fairy did not sleep.  It roamed
the land in a dreamless doze, lost and afraid amid a grim haze
of grey and darkness.  The fairy despaired.  It wanted no
part of this place.  It pretended for a time to be awake but
the bright daylight would not come.  It pretended for a time to
be dreaming but the colors and memories would not come.
That is when the fairy wished for oblivion.  Then just as
suddenly, it awoke in the daylight.  It fell to the ground,
stunned as if it had forgotten how to walk in the too bright
daylight.

Though the world again grew softer and kinder in time, the pixel
fairies were never the same.  For the night is dark and full
of terrors.

---

It used to be easy.  Screen on and screen off could explain almost
everything about the state of the device but it's different now with
ambient display.  We need to be able to wait for all windows to be
drawn even in the case where the device is still nominally asleep.
In truth, the window manager policy which drives a lot of these
interactions is a thicket of outdated assumptions.

Added a new method to tell the window manager policy when the screen
is being turned off so that it can correctly account for changes
to the interactive state (wakeUp and goingToSleep) and screen state
(screenTurningOn and screenTurnedOff).  Now we can independently
poke keyguard during interactive state changes and we can apply
screen on blocking during screen state changes.

Moved the code which manages screen on blocking (which is what
ensures the UI has fully drawn before revealing screen contents)
from the power manager to the display manager since the display
manager is in a better position to accurately track the state of
the screen, particularly when the screen is being turned off.

Fixed a bunch of synchronization issues.  Previously some work
had been moved to a handler without considering what might
happen if it became reordered relative to other work happening
elsewhere.  Documented the desired behavior in the code to
prevent this from happening again.

There's still a bunch of stuff in here that isn't quite right,
particularly the assumption that there's only one screen, but
it's good enough for now.  Hopefully there aren't too many bugs.

Bug: 17605802
Change-Id: Ic7319e09948c8a3cda014d7e169c964a3ad86f14