Return backwards compatible context versions in Vulkan, GL and D3D11. This allows us to pass some dEQP GLES 2.0 tests that require using an ES 3.0 context and matches native driver behaviour of returning a higher-than- requested context version when it's backwards compatible. BUG=angleproject:3425 BUG=angleproject:3300 BUG=angleproject:3715 BUG=angleproject:3243 BUG=angleproject:3240 BUG=angleproject:3716 Change-Id: I03dfd56deb6191c3363808717e0eea6fdcf5f3ac Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1709111 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>