Add a test for backwards mip generation with draw A test similar to mipmap generation with draw (mip0->mip1->etc) where a small mip is upscaled to lower mips with draw (mip2->mip1->mip0). Bug: angleproject:6977 Bug: b/229764351 Change-Id: Iff29f0e02af085c817c41f713644238edfcb22e8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3594803 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>