Adds an interface for classes which provider custom
handlers for features rendered as part of a map render job.
QgsRenderedFeatureHandlerInterface objects are registered
in the QgsMapSettings objects used to construct map render
jobs. During the rendering operation, the handleRenderedFeature()
method will be called once for every rendered feature, allowing
the handler to perform some custom task based on the provided
information.
They can be used for custom tasks which operate on a set of
rendered features, such as creating spatial indexes of the
location and rendered symbology bounding box of all features
rendered on a map.
