Grant access to Gamescope socket for Steam Deck

[rakonkido]

I encounter this error every time I launch a PPSSPP game through Steam Deck's Game Mode UI:

I've encountered it many times before when launching games through other Flatpaks, like those for Lutris, Heroic, and other emulators. Recently, I found that this error went away after adding support for HDR on Steam Deck to Lutris Flatpak -- itself based on the method used for enabling HDR support on Heroic and Chiaki4deck.

Similar to PRs I have made for RetroArch, Dolphin, and PrimeHack, I have tested and confirmed that just adding the gamescope-0 socket is enough to make the error go away, with no apparent regressions, if you have the Gamescope Flatpak installed:

flatpak install flathub org.freedesktop.Platform.VulkanLayer.gamescope

[flathubbot]

Started test build 94793

[flathubbot]

Build 94793 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/77541/org.ppsspp.PPSSPP.flatpakref

[flathubbot]

Started test build 94801

[flathubbot]

Build 94801 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/77549/org.ppsspp.PPSSPP.flatpakref

[bbhtt]

I approved the change but note that the socket is not fixed, there may be a gamescope-1 -2... and so on. But this is not something that can be solved with static permissions.

gamescope-0 should work for most cases