…cache. r=gw

We already have a cooldown from texture cache items being deallocated a certain amount of time and frames after their last use so we can deallocate texture arrays as soon as they are completely empty. We do this at the end of the frame to avoid deallocating and reallocating within the frame. It's better to reclaim texture memory this way than run into maybe_reclaim_shared_memory which will throw away everything and cause new allocations on the next frame.

Differential Revision: https://phabricator.services.mozilla.com/D68050

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/cb7a03e737951349193fb99410bb907991f7bc35