This now uses all the previously added features to allow displaying YUV
images.
Also add a utility function that turns an image into a toggle ref for a
texture. This makes sure that reffing the image also refs the texture
and that ensures that textures stay alive as long as the image is in
use.
For now, the flags are just there because, and nobody uses them yet.
The only flag is EXTERNAL, which for now I'm using for YUV buffers,
though it's a bit undefined what that means.
... and use it to initialize the "proper" projection matrix to use in
shaders.
The resulting viewport will go from top left (0,0) to bottom right
(width, height) and the z clipping plane will go from -10000 to 10000.
For now, it just renders using cairo, uploads the result to the GPU,
blits it onto the framebuffer and then is happy.
But it can do that using Vulkan and using GL (no idea which version).
The most important thing still missing is shaders.
It also has a bunch of copy/paste from the Vulkan renderer that isn't
used yet.
But I didn't want to rip it out and then try to copy it back later
