Marker: remove direct cairo usage

The first patch is straight forward: use our Transform methods rather than cr.rotate etc

The second patch is slightly more controversial for a couple of reasons:

1. I decided to just drop draw_ctx.clip() at the cost of a little bit of duplication since at least it is clear that it does not save/restore the cr.
2. we end up with a few nested dc.with_something methods... maybe this can be simplified out by just passing to draw functions the transform and the optional clip rect, but for now I think it is ok