Tiles no longer hog the queue ahead of all else.
We now give priority to callback events, so clients
get to know the document state sooner.
Since tiles take long to render, an equal time
is given to non-tiles (capped at 100ms).
Finally, Impress preview tiles are given
the lowest priority and rendered only when
the queue is drained.
Change-Id: I922c1e11200e5675f50d86b83baee1588cbbf66f
Reviewed-on: https://gerrit.libreoffice.org/31394
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>
Tested-by: Ashod Nakashian <ashnakash@gmail.com>
