Encapsulate prevTexture pointer in a class * Encapsulated mPrevUploadedMutableTexture from ShareGroupVk into the new TextureUpload class. Bug: chromium:1346808 Change-Id: Ied52071d4e7f624fc2c497c4086b2589b840561d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3813032 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>