Feature Request: Add highlights spanning facets

[snystrom]

The goal of this visualization is to draw a rectangular box spanning facet boundaries for the purpose of highlighting a range of data along a continuous scale.

I think this would be a relatively straightforward addition (perhaps even from extending facet_zoom code) which would have many practical applications.

Examples of this can be found here:
Here

You could also imagine this being a useful geom for allowing facet_zoom() on a faceted plot where the highlight rectangle is drawn by the highlight geom and the zoom-expansion highlight is drawn by facet_zoom.

[thomasp85]

As this doesn't fall under the standard things you can do with the ggplot2 API (graphics spanning panels) it is unlikely to get into ggforce so I'm closing it