We were storing the resolved pixels in all cases, but nr_samples > 0 means
we should be keeping the per-sample values.
We will probably want to change the job structure at some point, as we'll
want to recognize full-buffer resolves and do the resolved store in the
same job as the original rendering, meaning we'll need to track both the
MSAA and single-sample resources in the job. However, this will be enough
to build the rest of the MSAA support.
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