v.in.csv: Add reprojection support using pure GRASS

[wenzeslaus]

v.in.csv currently requires pyproj. It would be better if it is handled without additional dependency using m.proj or different GRASS location.

This was also mentioned in the original PR by @mlennert.

As I noted in that discussion, having an API for the location-reprojection exercise (such as Session in a temporary location) would be desired to avoid duplicating the v.import functionality. Alternatively, m.proj may work, but there might be a reason why I did not use it.

[wenzeslaus]

Notably, I'm not assigning this to myself and the issue is up for grabs. Given that the ideal solution includes better API in code, this might not be a good fit for complete beginners, but it is a good issue if you already know some GRASS or are comfortable with Python.