Run PackUnpackTest on all backends Fixed negative zero serialization for capture/replay. Bug: angleproject:4092 Change-Id: Ic12a556f56e40064da8bf3a8ce7d01af92c7086a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5106509 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>