Games crash or stutter when vulkan-loader is missing

[piedar]

Recently I noticed major issues with games running via Proton.

• failure to launch except with old Proton 5 and PROTON_USE_WINED3D=1
• crashes, stuttering, and very poor performance

In the Steam output I saw

Vulkan missing requested extension 'VK_KHR_xlib_surface'.
BInit - Unable to initialize Vulkan!

so I installed media-libs/vulkan-loader[X, abi_x86_32] and now games run smoothly with the latest Proton Experimental.

Should this be added as a dependency?