Modify get_urbn_map() to use tigris + shift_geometry().

[ajjitn]

Right now we manually ellide AK and HI to be inset below the continental US. But the recent version of the tigris package now offers the powerful shift_geo function to shift AK and HI states to be inset. I think it would be a good idea to use the tigris functions - with some smart defaults like resolution = "5m" and cb = T - to be the backend for get_urbn_map() because it would allow other points/geographies to be easily ellided with the same shift_geo() function to display properly in AK and HI.

There are some disadvantages we would have to think through including

1. The shift_geometry() function automatically converts the CRS to ESRI:102003 (Albers Equal Area), instead of the National Atlas Equal Earth projection we currently use. This is in line with the Urban style guide but could be a breaking change for others.

2. The positions of AK and HI in tigris (in blue) are slightly different than our old defaults (in magenta).