feature: add dodge transform

[gka]

Is your feature request related to a problem? Please describe.
see Dodge transform in Observable Plot.

Describe the solution you'd like
The dodge transform needs to be applied after scaling, so it can't be passed to the marks like other transforms. Instead we could allow users to pass a dodgeX or dodgeY property to all applicable marks, e.g.:

<!-- just activate dodgeY -->
<DotX data={cars} x="weight (lb)" fill dodgeY />
<!-- or pass anchor options: -->
<DotX data={cars} x="weight (lb)" fill dodgeY={{ anchor: 'bottom', padding: 2 }} />