Our current FileAutocomplete widget works, but I personally find it clunky and limited. Let's try to improve it by making something that is more like a traditional filechooser with "Recent" and other shortcuts.

The basic idea is that there is a TextInput in a dialog with a "Browse" button, in the same place as the normal dropdown toggle. When that is clicked, a pretty large dropdown opens that contains the filechooser. It stays open and let's the user interact with it until it is explicitly dismissed.

Instead of a dropdown, the filechooser could also be inline expanded/collapsed in the dialog, or even temporarily replace the current dialog completely. The mobile layout should determine what works best. Maybe we do different things in different layouts.

The filechooser has buttons that navigate to certain places or virtual collections, like "Recent", "Home", all the interesting pools, etc.

There should be buttons to create new files and volumes, or maybe there are strict "no-create" and "create-only" modes for it.

The goal is to use this widget for the primary disk image when creating a VM, for the disk image when adding a new virtual disk, and to select local install media.

The widget should be trivially usable with `cockpit/dialog`.