Add wl_shm support for 10 bpc formats and wl_shm/DMA-BUF support for 16 bpc half float formats

This makes it possible to create 10 bpc as well as 16 bpc wl_shm buffers (e.g. WL_SHM_FORMAT_ABGR2101010 and WL_SHM_FORMAT_ABGR16161616F). Both variants can be tested either using the gradient-test test client.

The 10 bpc formats can be tested with mesa upstream, while the 16 bpc formats currently requires patches. Both using software rendering via wl_shm and llvmpipe ad hardware accelerated rendering via DMA-BUF should work.

Marking as WIP as it currently depends on an unreleased wayland-server.pc.