--export-area-page should be updated for multiple pages

Summary:

Now that Inkscape 1.2 has support for multiple pages per SVG document, it would be really nice if the command-line option --export-area-page were updated to allow choosing which page to export. (Or at least make a note in the man page that only the default page is exported.)

Steps to reproduce:

Make a multi-page SVG. Run inkscape --export-type=png --export-area-page.

What happened?

It exports the page defined by the SVG viewBox. As far as I can tell that is always one of the pages defined by inkscape:page, though it does not have to be the first page.

What should have happened?

Well, --export-area-page alone should continue to export the viewBox area. But I'd like a command-line option to export selected pages other than the viewBox one. For example, allow it to take an optional argument: --export-area-page=2.

Note that for backward compatibility --export-area-page should not be equivalent to --export-area-page=1 because after rearranging and renumbering pages, Inkscape's "page 1" does not necessarily correspond to the page defined by the SVG viewBox. When the page number is omitted it should continue to export the viewBox area.

Version info

Inkscape 1.2.2 (b0a8486541, 2022-12-01)

    GLib version:     2.74.1
    GTK version:      3.24.36
    glibmm version:   2.66.5
    gtkmm version:    3.24.7
    libxml2 version:  2.10.3
    libxslt version:  1.1.37
    Cairo version:    1.17.6
    Pango version:    1.50.12
    HarfBuzz version: 5.2.0

    OS version:       Fedora Linux 37 (Workstation Edition)