Add Envelope::fromXY

[dbaston]

Per discussion in https://lists.osgeo.org/pipermail/geos-devel/2020-November/009882.html

[dr-jts]

Ok yes, this is one way to add a different parameter order. But you have to know this method exists and that you need to use it - which seems to have the same cognitive cost as simply using the current parameter order in the constructor! I guess it does help to highlight the unconventional order of the constructor params though.

[dbaston]

Yeah, not sure changing the parameter order is worth it. I do think having a constructor that assumes sorted inputs (xmin, xmax) vs (x1, x2) is worthwhile.