Relax the parens requirement for multipoint

[audunska]

Postgis' ST_AsText function will serialize multipoints like MULTIPOINT(0 1, 2 3), which would fail to deserialize because we expect a string like MULTIPOINT((0 1), (2 3)).

In fact, the Postgis ST_GeomFromText function even accepts mixed bracketing, like MULTIPOINT((0 1), 2 3).

This PR updates the parsing of multipoints to allow all these styles.

• [x] I agree to follow the project's code of conduct.

• [x] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

[michaelkirk]

bors r+

[bors[bot]]

Build succeeded:

• wkt