Focusing with ctrl-f shouldn't keep the search pattern

[Canop]

When searching on a path, and focusing a deep file, we often end up without the deep file matched because its path relative to the new root doesn't match anymore.

Moreover, it's easy to search again now that broot has ctrl-f.

Focusing a deep path should:

• make the closest directory the new root (no change from current behavior)
• remove any search pattern (it can be restored with ctrl-f)
• try select the path which was selected before focus