Zoom to data

[arcresu]

Previously there was a coord_automap_zoom() that used a hacky workaround to give a sensible default zoom. The idea is that the normal ggplot2::coord_sf() keeps track of the bounding box but doesn't discriminate between layers, so adding the base map with geom_boundaries() ends up making the bounding box too big. In some cases that's what was intended, but in other cases it can be nice to zoom into the area bounding the actual data (excluding the base map).

This was originally done with a hack that doesn't adhere to the ggplot layer structure. Ideally it would something like coord_automap(zoom = "data") rather than a separate function. The coord will probably need to gain a concept of "base maps" and track two different bounding boxes.