Vulkan: reserve extra varyings when basicGLLineRasterization or supportsTransformFeedbackExtension is enabled. updated with MaxVaryingWithFeedbackAndGLline adding test to validate pixel value (disabled for macos) Bug: angleproject:4273 Change-Id: Ie3d3516fd3806c0d622fb402ba8223d302206f73 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2071237 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>