Roadmap for wl-mirror 1.0.0

[Ferdi265]

This issue is a meta-issue summarizing the general direction of wl-mirror and what is required for me to consider the project ready for 1.0.0

Showstoppers

These issues absolutely need to be fixed before I can consider wl-mirror ready for 1.0.0.

• #16 Support for XDG Desktop Portal Screensharing
• #17 Support for other compositors, mainly KDE and Gnome
• #61 Support for individual window capture