This commit refactors all spatial Field Mappers to a common
AbstractGeometryFieldMapper that implements shared parameter functionality
(e.g., ignore_malformed, ignore_z_value) and provides a common framework for
overriding type parsing, and building in xpack. Common shape functionality is
implemented in a new AbstractShapeGeometryFieldMapper that is reused and
overridden in GeoShapeFieldMapper, GeoShapeFieldMapperWithDocValues,
LegacyGeoShapeFieldMapper, and ShapeFieldMapper. This abstraction provides a
reusable foundation for adding new xpack features; such as coordinate reference
system support.