This will be replaced by the previous UI: two buttons, "Open" to open
the dialog, and an arrow to open the recent menu.

It's a pragmatic decision to simplify the gedit code, because there are
not enough developers, and too many bugs. Do you prefer a rock-solid
text editor? Or a text editor with some shiny and non-essential features
that complexifies the code, at the expense of more bugs? The gedit core
should have a much smaller code size, with all the essential features
implemented in libraries.

The OpenDocumentSelector showed only 5 items, while the normal menu can
show more (10 by default).

The search inside the popover duplicated the search in the file chooser
dialog. To open a file, one search entry is enough, it avoids a possible
confusion.

The OpenDocumentSelector showed all recent text files, not just those
previously opened in gedit. Again, this duplicates the feature present
in the file chooser dialog. The new simple menu will show only files
previously opened in gedit, which is IMHO more logical.

There is also the fact that the OpenDocumentSelector used GtkTreeView.
It is planned at some point in the future that GtkTreeView will be
removed from GTK. Porting to GtkListBox would be a lot of work.

The full file paths will also be visible with the new simple menu, in
the statusbar.

GeditOpenDocumentSelector was never adopted by other GNOME apps. gedit
was the only app with such an open file popover. It takes almost 3000
lines of code to do so. While the simple menu takes less than 100's (in
gedit). So the OpenDocumentSelector complicated a lot the code of gedit.