`GEOSisValidReason_r` doesn't construct reason string with Z/M coordinate values

[scottrhoyt]

It looks like the issue is here where the coordinate is referenced explicitly as XY. While Z/M coordinates may not contribute to whatever the invalid reasoning is, it would be clearer to the user to return the full coordinate they passed in.

[dbaston]

It's not that single reference, it's the entire validity checking process which is 2D-only.