libgproj: Use SRID for PJ object creation when possible

[HuidaeCho]

This PR tries to address #2257 by using SRID, not GRASS key-value pairs, for creating an PJ object. Here is a related Q&A.

[HuidaeCho]

@metzm Do we ever hit this PROJ error when pj is already not NULL? https://github.com/OSGeo/grass/blob/830f31d215038c1a67112aa350619f652e04e70b/lib/proj/get_proj.c#L275-L278

[HuidaeCho]

@metzm Do we ever hit this PROJ error when pj is already not NULL?

https://github.com/OSGeo/grass/blob/830f31d215038c1a67112aa350619f652e04e70b/lib/proj/get_proj.c#L275-L278

I think we can remove this check.

https://proj.org/development/reference/functions.html#c.proj_create_argv

If creation of the transformation object fails, the function returns 0 and the PROJ error number is updated.

[metzm]

Apparently proj_errno(pj) can still return an error code, if pj is not NULL. At least this is used in various places in PROJ itself.