[Feature] Further break down macOS memory usage

[ClementTsang]

Checklist

• I've looked through the documentation and existing open issues for this feature/feature request.

Describe the feature request

Original: #1043

After #1036, macOS memory usage matches Activity Monitor (at least on m1, need to test on x86). However, it just dumps one lump sum of "usage", which is often pinned near 100%, which isn't useful, as it sums memory used + cached files. It might be useful to be like Activity Monitor and display the uses split + combined, or at least investigate if it's doable.