Previously, before emitting a `Focus` event from the pane inside of the
`focus_in` listener, we would erroneously check whether the pane's focus
handle was _not_ focused. However, by the time the pane was notified of
being "focused in", the focus handle would already be focused, which was
preventing the pane from ever emitting a `Focus` event. In turn, this
would cause the workspace to not maintain the active pane correctly.

This pull request maintains an explicit `was_focused` boolean as part of
the `Pane` state, which ensures we only emit the `Focus` event the first
time the pane receives focus.

As part of this, I also reworked how the outline view gets deployed to
allow clicking breadcrumbs even when the corresponding pane doesn't have
focus.

Release Notes:

- N/A