Feature: Use DynamicLauncher to automatically install desktop files for extensions

Using https://flatpak.github.io/xdg-desktop-portal/#gdbus-org.freedesktop.portal.DynamicLauncher
It might be possible to have the steam flatpak automatically install desktop files for extensions.

This would allow users to easily launch apps(extensions) like:

https://github.com/sonic2kk/steamtinkerlaunch
https://github.com/alvr-org/ALVR

Start with the DynamicLauncher specification linked in the issue and inspect how the Steam Flatpak handles extension integration and desktop files. Compare the desired behavior with steamtinkerlaunch and ALVR, then define acceptance checks for launching those extensions from installed desktop entries. No repository file or test is identified, so expect project-level investigation first.

Written by the indexing model from the issue text.