Can't mark workspace

**Description:**
One can mark the workspace in i3 but not Sway. This is due to Sway managing the workspace as separate and distinct from containers, whereas in i3 the workspace is a container.

**Impact:**
This breaks the ability to move containers up the tree when the destination is the workspace. See #6903 and #8418 for details. I can't say for sure rn whether this impacts other use-cases.