dEQP: Enable CreateSurfacePlatformEXT tests Add the corresponding capability to NativeWindow and implement getPlatformExtension virtual method to return a native pointer that can be used with eglCreatePlatformWindowSurfaceEXT(). Bug: angleproject:6961 Change-Id: Ieb1a1fd8b3cae4e6f199c269f3922cbd0307aa35 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3452102 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Auto-Submit: Antonio Caggiano <antonio.caggiano@collabora.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>