[//gpu] Pass MacOS-specific texture target in SharedImageCapabilities

ClientSharedImage will use this field where it currently uses the
global `macos_specific_texture_target` in GetTextureTarget(). This will
enable decoupling ClientSharedImage::GetTextureTarget() from
GetPlatformSpecificTextureTarget() and eventually eliminating the
latter, as well as the global `macos_specific_texture_target` itself and
all the infrastructure around it.

Note that there is no new info being passed between processes here, as
this state is already available in all processes via
GetPlatformSpecificTextureTarget().

Bug: 41494843
Change-Id: I834daae539553af0871166503e998968b0c94ebc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5397778


Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278993}