[TreesInViz] Serialize deleted tiles and tilings from pending tree updates.

Add ability to serialize deleted tiles and tilings from pending tree
updates. When a tile/tiling is deleted in pending tree, it is sent as a
part of next tree update. But by the time next update is serialized by
client, the tiles/tilings might have already been deleted and removed
from client side.

This CL adds ability to create a serialized version of deleted tile and
tilings from pending tree updates which can be sent to service/viz side.

Bug: 418264487
Change-Id: Icf0aa3ac680fc90f3b2e1dbd88e64f021cffce4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6558708
Reviewed-by: Victor Miura <vmiura@chromium.org>
Auto-Submit: vikas soni <vikassoni@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: vikas soni <vikassoni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1464611}