Vulkan: fix ASSERT issue in ResourceSerialFactory Refactor ResourceSerialFactory::issueSerial so that the ASSERT is valid in a threaded environment. Otherwise it's possible for another thread to increment mCurrentUniqueSerial in the middle of the ASSERT. Bug: b/168744561 Change-Id: I7208e8be91b21c50ad4a260d02d69f5b7dab2efe Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2426685 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>