[AndroidTV] Add an option to regroup directories and files browsing under the same alphabet listing

Description

Right now, browsing views display directories and files separately.

On Android TV views, the items are regrouped by the first letter of their name.

As a consequence, this leads to a "double alphabet" listing (one for the directories, one for the files), both on grid and list view.

Expected behavior

On this particular "alphabet list" grouping, it could be convenient to add an action to regroup both directories and files under the same "alphabet listing".

This could also make the "Jump to" action more friendly (no confusion on the double alphabet display).

Note that this is more significant on the AndroidTV application, where scrolling is harder to perform (than on a smartphone, for example).