* Move workspace selection into separate function
* Instead of keeping a `prev_focus` variable, do the check in
`should_focus` (ie. views can only take focus if they're mapped into the
active workspace)
* Fix assign-to-output - it previously set `prev_focus` but should be
`target_sibling`
* Remove call to `workspace_switch` as we'll only ever focus the view if
it's in the active workspace
a90f2dbde9