In support of tracking compressed texture data across multiple
threads and contexts, move our cache to FrameCaptureShared.
Make this accessible only via egl::ShareGroup, which will
ensure unique texture IDs.

Test: Asphalt 8 MEC
Bug: b/150484427
Bug: angleproject:4048
Change-Id: I4e75b323d7aedc0333ceffba305439e54c4d6ac1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2455266
Commit-Queue: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>