Add support for playing HDR games

This uses a protocol that's cut down from the upstream proposal, so that we can merge it quickly and use it for more extensive testing, and for playing games, until the upstream protocol is merged.

To test this, install https://github.com/Zamundaaa/VK_hdr_layer. Then enable HDR on your monitor if you haven't already, for example like this

kscreen-doctor output.1.wcg.enable output.1.hdr.enable output.1.sdr-brightness.500

and run Quake 2 RTX with SDL_VIDEODRIVER=wayland ENABLE_HDR_WSI=1 set.

For games that aren't Linux native, build !4566 (merged) and gamescope from git master with

ENABLE_HDR_WSI=1 gamescope --hdr-enabled --hdr-debug-force-output --steam -- env ENABLE_GAMESCOPE_WSI=1 DXVK_HDR=1 DISABLE_HDR_WSI=1 steam -bigpicture

Note that a bunch of games, like Doom Eternal, require an EDID to parse for HDR to work. That's not implemented yet outside of gamescope's embedded mode, so HDR will not work in these games yet until that's done. Cyberpunk 2077 for example does not need that though, so it can be played without issues: