Screenshot portal for elementary 8 should be backported for 7.1

[phase1geo]

What Happened?

When I attempt to use the screenshot portal when running on elementary OS 7.1, the screenshot panel is sometimes hidden behind other windows and/or not centered in the display and taking a screenshot with it returns an error to the requesting application instead of a valid image. The OS 8 implementation seems to be working properly in my testing.

Steps to Reproduce

With the following code:

portal.take_screenshot.begin( parent, Xdp.ScreenshotFlags.INTERACTIVE, null, (obj, res) => {
      try {
        var screenshot = portal.take_screenshot.end( res );
        var file       = File.new_for_uri( screenshot );
        ...
      } catch( Error e ) {
        stdout.printf( "ERROR: %s\n", e.message );
      }
    });

The portal for elementary 7.1 causes the "catch" code to execute with the message of "Screenshot failed" (or something close to that).

Expected Behavior

The expected behavior can be seen on elementary OS 8 RC which returns a valid screenshot file image that can be used by the calling application.

OS Version

7.x (Horus)

Session Type

Classic Session (X11, This is the default)

Software Version

Latest release (I have run all updates)

Log Output

No response

Hardware Info

No response