Because feature.geometry().geometry() is confusing, and impossible
to search for in python code (e.g. is input.geometry() a QgsGeometry
or a QgsAbstractGeometry?)
But more importantantly: also add a const version
QgsGeometry::constGet(). The non-const
version is slow, since it now forces a detach to avoid corrupting
geometries (since QgsGeometry is shared, it's not safe to directly
access its primitive QgsAbstractGeometry and start messing with
it without first detaching). This is a big risk in the 2.x API
which could potentially corrupt feature geometries with unexpected
outcomes.
Update all uses to constGet where possible.
