Refactor more Texture entry points to a consistent style. TexImage, SubImage and the Compressed variants were all taking a GL Context as the first parameter, which is a layering violation and also caused problems with reworking how the sync works. Fix this by refactoring them in the same style as the CopyTex* entry points. BUG=angleproject:1260 BUG=angleproject:747 Change-Id: Ibe5e87d0ebc790e2dcadb8ba153cf40fec73d1f6 Reviewed-on: https://chromium-review.googlesource.com/327258 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>