Async BLAST Sync[4/N]: Replace draw handlers with seqId

Our current model for draw handlers use relayoutWindow to correlate
calls to finishDrawing with specific states. Namely all states
that were changed by the time relayoutWindow returned, will be
included in the next finishDrawing. This is the meaning of
the mPending and mCurrent draw handlers. Any draw handlers
(and assosciate state change) added after a call to relayout
wont be observed by the client, and so we dont want to
execute the draw handler when we receive finish drawing. See
BLASTSync.md for a detailed discussion. Understanding that the previous
code simply only executes draw handlers which were added after relayout
we can see that the new code does the same thing. Draw handlers which
are executed must have a seqId less than the one returned from the
relayout immediately proceeding finishDrawing, and so it must be the
same set of draw handlers which were added before relayout. Again
see BLASTSync.md for a detailed discussion of why this is expected
to work even without relayoutWindow

Bug: 161810301
Bug: 175861051
Bug: 175861127
Bug: 200285149
Change-Id: Icd36129927da32fb175ea9071319b06d4d1475a7