WindowState: applyWithNextDraw fixes

In this CL we make a few fixes to harden applyWithNextDraw.

1. Currently there is a bug where we apply the transaction directly
   in executeDrawHandlers, this breaks BLAST sync as we need to pass
   the post draw transaction on, not apply it.
2. When we pass it on, we expose a bug in WindowStateAnimator#finishDrawing
   if the state is DRAW_PENDING we merge to mPostDrawTransaction instead
   of applying, but mPostDrawTransaction is only applied if mLastHidden
   is true. Rotation resets mDrawState=DRAW_PENDING but doesnt reset
   mLastHidden so this means transactions that end up in
   mPostDrawTransaction as a result of rotation would be lost. We modify
   finishDrawing to check mLastHidden and see if we will apply later.
3. The timing of prepareDrawHandlers should be moved to the end of
   relayout, so that calling it works while in relayout.
4. We should clear mRedrawForSyncReported when preparingDrawHandlers, if
   the client got the changes in relayout we dont need the client to
   call relayout again.
5. Add a big comment explaining how all this works.

Bug: 168505645
Test: Existing tests pass
Change-Id: Icd79cc98abb01c73cecff053ef9ca990034d0891