This is a reland of 4e37751693
Original change's description:
> Make it easier to test rectangle textures by using createBackendTexture.
>
> Also allows internal creation of rectangle textures, only used by unit
> tests currently.
>
> Previously GrContext::createBackendTexture() would ignore the request
> for RECTANGLE or EXTERNAL and always make 2D. Now it makes RECTANGLE if
> supported and always fails for EXTERNAL.
>
> Change-Id: Iafbb3f5acddb37bfb8d39740f2590177a07dae78
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297472
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>
Change-Id: Ibf6921c97278c9f0f71c46883cfbaa04f229affa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297865
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>