[//content] Convert SI RASTER usage to RASTER_READ | RASTER_WRITE

There are no functional changes, as RASTER is a constant that expands
to RASTER_READ | RASTER_WRITE. This will allow us to subsequently (1)
eliminate RASTER and (2) refine all RASTER_READ | RASTER_WRITE usage
based on where raster reads and writes are actually necessary.

Bug: 1519074
Change-Id: I61a882ad741efb7aeb5afd56347c340c212a4222
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5210411
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1248658}