In addition to resolving issues with mixing HDR and SDR displays and moving
between them while streaming, it also allows streaming HDR content to an SDR
display with tone mapping handled transparently by libplacebo.
Vulkan H.264/HEVC video decoding isn't supported with Fedora's Mesa binaries due to
patent issues, so only the VAAPI/DRM-PRIME import path was tested locally with ANV.
HDR video is getting tonemapped to my SDR monitor reasonably, so HDR output probably
works with GameScope but I haven't confirmed yet.
See #1117