zink: implement shader precompiling (AS SEEN ON YOUTUBE)

the pipe_context::link_shader hook is called when shaders are
linked into a program by the application

by leveraging this, it becomes possible to utilize the existing
graphics pipeline library to implement precompilation
by creating a partial pipeline containing only the shader stages
and then adding in the vertex input and fragment output stages
dynamically using the fast-link feature

if all goes well, and if the vulkan driver's fast-linking is
truly fast, the full pipeline should be dynamically combined
in time to avoid stuttering, and an optimized variant will be
queued for async compile to be used the next time the pipeline
triggers a draw