…idity checking of geometries.

The ValidOp module provides methods based on simple geometric predicates to determine validity for a geometry and can be used as a fallback or overridden.
The module can be overriden fully (in the case of Cartesian polygons) or just by implementing #invalid_reason (FFI and CAPI factories).

Removes #validate_geometry from all classes and replaces them with #prepare_geometry. Any required validations were moved to the constructors.

Adds the ValidityTest module to test/common to ensure that all classes of geometries validate in the same way.

…ommon module

ValidOp is to be included in feature classes and has the invalid_reason and valid? methods, as well as feature type specific methods that walk through the validity flow for each
geometry type.

ValidOpHelpers is a collection of functions where an object is passed to them. These perform the specific checks and return the invalid reason if applicable.

Also added overrides for both modules for cartesian functions.

…nd fix tests, ValidOp so the spherical factory passes validity checks