rendernode: Create Cairo surfaces as recording surfaces

rendernode: Create Cairo surfaces as recording surfaces

This way, we can postpone the actual rendeing of the node until the
renderer. This allows the renderer to choose the right scale to
render at, so it can decide to use 2x scale for hidpi on its own.

Last but not least, it makes all nodes independent of the context they
are created in, because they do not need to know at snapshot time what
they will ultimately be rendered into.