This heaves over an inital chunk of code from the Vulkan renderer to
execute shaders.
The only shader that exists for now is a shader that draws a single
texture.
We use that to replace the blit op we were doing before.
Add a bunch of inline functions for graphene_rectangle_t.
We use those quite extensively in tight loops so making them as fast as
possible via inlining has massive benefits.
The current render-heavy benchmark I am playing (th paris-30k in node-editor)
went from 49fps to 85fps on my AMD.
