Add action buttons to the file browser toolbar when selecting items

[jtpio]

#6377 added support for displaying file browser checkboxes by default in Notebook v7.

A nice follow-up would be to add something similar to the classic notebook, with action buttons in the toolbar:

checkboxes-buttons.mp4

These actions are already accessible via the context menu, but could still be nice to have in the toolbar so they are more visible.

[jtpio]

These actions are already accessible via the context menu, but could still be nice to have in the toolbar so they are more visible.

This would also be useful on mobile devices.