PostGIS 3.1+ support

[peetw]

Running the Tests.NHibernate.Spatial.PostGis20 tests with PostGIS 3.1+ fails with the following error:

OneTimeSetUp: NHibernate.HibernateException : 42883: function st_intersection(geometry, geometry) does not exist
  ----> Npgsql.PostgresException : 42883: function st_intersection(geometry, geometry) does not exist
Data:
  Severity: ERROR
  SqlState: 42883
  Code: 42883
  MessageText: function st_intersection(geometry, geometry) does not exist
  File: d:\pginstaller_12.auto\postgres.windows-x64\src\backend\catalog\pg_aggregate.c
  Line: 871
  Routine: lookup_agg_function

[peetw]

Seems to be caused by the following SQL statement:

CREATE AGGREGATE NHSP_IntersectionAggregate(BASETYPE=GEOMETRY, SFUNC=ST_Intersection, STYPE=GEOMETRY);

[peetw]

The error is caused by the fact that the signature for ST_Intersection changed in PostGIS 3.1 - it now has an optional gridSize parameter (see here and here). Therefore, will need to conditionally create a wrapper around the new function depending on the PostGIS version.

[peetw]

Fixing the intersection aggregate issue reveals that tests ConformanceItemT48Hql and ConformanceItemT48Linq are also failing with PostGIS 3.1, but this looks to be due to the ordering of the returned polygon co-ordinates - using EqualsTopologically rather than EqualsExact resolves the issue

[andrerav]

Great work @peetw! 🙏