containments/desktop/plugins/folder: Add ability to hide desktop icons for containments

This MR adds an option to hide icons in a folder view, for containments only, similarly to how the locked feature is implemented. This is useful for when a user may want to temporarily hide their desktop icons, maybe when showing their desktop in a recording or screen-sharing - private files may exist on their desktops.

Any recommended changes are welcome, there was a lot of work following through different files and I'm not completely confident that things are perfect.