support vk hdr mode

[hanatos]

this is tightly related to wayland colour management, which is unfortunately not ready in compositors. for hdr mode, one has to enable it in say hyprland:

experimental:hdr=true
experimental:wide_color_gamut=true
experimental:xx_color_management_v4=true

install VK_hdr_layer https://github.com/Zamundaaa/VK_hdr_layer.git, then in vkdt: enable the layer, attach hdr metadata to the swapchain, and encode HLG in the frame buffers.

initial experiments show that this is working (with some caveats), but needs runtime switches and some validation with a colorimeter.