SW Image Decode Cache Low to Medium Quality for Downscale
When using the SW Image Decode Cache, low quality images are kept at
full resolution, and scaled at raster time using a low-quality filter.
While this is cheap from a performance standpoint (no decode-time
scale), it increases the cost of storing these images, as they are
always stored at full resolution.
This change causes us to use medium quality scaling for images which
request a low quality downscale. This will generate a mip-level scale,
and cache that, potentially reducing our cache size.
While this could have a performance cost, this is already the path
used by the GPU cache, and we haven't observed performance problems