Add makeCurrent and unMakeCurrent to SurfaceImpl. SurfaceGL had these methods already so they are just moving up the inheritance hierarchy. This ends up simplifying some state tracking we had in our surface implementations. BUG=angleproject:2464 Change-Id: I480588ca8470d9ef507f95e0c0297fe126b3abfb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1595434 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>