This is a reland of d617d5d29c
Original change's description:
> Update DEPS: roll spirv-tools and spirv-headers.
>
> spirv-tools and spirv-headers were about two years out-of-date, and
> Dawn requires more recent versions.
>
> This required an updated BUILD.gn file for spirv-tools. I used a
> modified version of the one I had written for Dawn. (The latter will
> be removed in favour of this one when we switch the Dawn backend
> from using Dawn's DEPS for spirv-tools and spirv-headers to using
> Skia's).
>
> Change-Id: If61eb05ada9f4287b1a16daf10f9b1fac041a7b0
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234907
> Commit-Queue: Stephen White <senorblanco@chromium.org>
> Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Change-Id: Ic4fe17fe286b04905977b9acb280ee9970b305bc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/237194
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
238fc249a4