Sets the coordinate transform which will be used to transform
the feature's geometries.
If this transform is valid then it will always be used to transform
features, regardless of the destinationCrs() setting or the underlying
feature source's actual CRS.
This method should be used with caution, and it is recommended
to use the high-level setDestinationCrs() method instead. Setting a specific
transform should only be done when there is a requirement to use a particular
transform, eg when a specific, non-default coordinate operation
MUST be used for the transformation.
