That's a second deprecation of this API in a short while, sorry. This
variant is hopefully the final one, with the previous one I still had
the problem that it contained a verb, which implied that it'd
*transform* the SceneData in some way which (unlike combineFields(),
filterFields() etc.) it didn't, it just extracts some data in a certain
way. This would all cause problems when there are APIs that actually do
perform hierarchy flattening.
It's also moved to a new, more general Hierarchy.h header which will
contain other hierarchy-related APIs. It doesn't make sense to have a
tiny header with just a single function, especially given it doesn't
depend on any heavy headers on its own.
Besides that it also makes the UnsignedInt overloads the main ones, and
the Trade::SceneField secondary, as is already done everywhere else (and
the opposite way was just bad inheritance from flattenMeshHierarchy()
it seems).