Loading data in EPGS:4326 across the antimeridian results in non-intuitive outcomes

[caitlinadams]

Loading scenes in EPSG:4326 across the antimeridian results in an xarray that spans the globe containing mostly zeros.

dc.load should raise a warning if users load data around the antimeridian in EPSG:4326 or EPSG:3857.

drivers/postgis/_spatial contains code to repair spatial extent in cases of loading in EPSG:3857. This code should be moved to a utility library, then called in the driver code (it should also perform the repair action for EPSG4326). That code can then be used in dc.load to provide a warning to the user if they geometry of their query comes back as a multipolygon.