Make focus mode accessible from the template editor

In the Site Editor it's possible to edit template parts in isolation like so:


https://user-images.githubusercontent.com/846565/162429505-8be90a95-22c2-4deb-b79a-3aecd3120540.mp4


However it's not possible to access this mode in the template editor (Edit post > Open 'Template' Inspector panel > click 'Edit'), should it be?