toContentScale
Converts AsyncImage's own nested ContentScale enum into its Compose ContentScale counterpart. A distinct type from ImageContentScaleSchema.toContentScale below despite the identical set of cases — AsyncImage and Image each declare their own ContentScale type on the wire, so their DSL helpers (cropContentScale() vs imageCropContentScale(), etc.) aren't interchangeable either.
Converts Image's own nested ContentScale enum into its Compose ContentScale counterpart — see AsyncContentScaleSchema.toContentScale above for why this is a separate function rather than a shared one.