Handle MultiPolygon in Polygon layers

[dalmijn]

Feature type

Adding new functionality

Improvement Description

Shapefiles are able to incorporate MultiPolygons in a layer that is designated to 'only' have Polygons.
When copying the layer information to a new Dataset and adding the geometries with addiotional fields, it produces an annoying (but valid) warning. With the high probability that some drivers simply won't accept it. Have not tested that. Got the the warning while using the GeoPackage driver.

Implementation Description

To be determined.

Additional Context

No response