FrameCapture: Handle glReadPixels with pack buffer
FrameCapture: Handle glReadPixels with pack buffer

Test: Capture PUBG Mobile
Bug: b/159238311
Bug: b/165824228
Change-Id: I3d76e0ccd641616ba971f15ed6ea280c4905fe18
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2503473
Commit-Queue: Cody Northrop <94770d7fe1cce6ea0791fa9927c1107de4d2e37b@google.com>
Reviewed-by: Courtney Goeltzenleuchter <aa371ec5c940a0ded89f7ed95bce84faebcf51df@google.com>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle