Goals:
- Extensibility: we need to be able to add new params to the calls to render a texture/rect. For instance we'll need to add fences to the render texture operation for explicit sync purposes.
- No implicit state: no more bind_buffer, begin, end.
- No matrices: these hurt Pixman and we don't need them.
- Clip regions for optimized damage repainting.
Closes: #3188
It was about time we broke that API.