[gpu] Post delayed flush task through ThreadPool for DestroySharedImage

When clients currently call SIInterface::DestroySharedImage they
need to explicitly call SIInterface::Flush as that will flush the
deferred destroy request.

This change adds capability to PostDelayedTask using ThreadPool so
that the DestroySharedImage deferred task(s) can be batched and
flushed together after a certain delay.

After this, we can avoid calling SIInterface::Flush that is needed
for such DestroySharedImage cases.

Bug: 399387909
Change-Id: I079d6a8c30e9a1303ba94916177ed2f269278d5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6302849
Commit-Queue: Saifuddin Hitawala <hitawala@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1425993}