This is based on the API that will be used for no-copy presentation. But
wraps it in `set_buffer`.
This also fixes the Wayland buffer code to set `self.width` and
`self.height` on resize, and set the length of the shared memory file
when the buffer is created.
Co-authored-by: jtnunley <jtnunley01@gmail.com>
A limitation of this implementation is that it can't coexist with anything which creates a canvas context other than `CanvasRenderingContext2D`, since only one context can exist per canvas.
