Introduce class parent_map for DIE range map

This changes the DIE range map from a raw addrmap to a custom class.
A new type is used to represent the ranges, in an attempt to gain a
little type safety as well.

Note that the new code includes a map-of-maps type.  This is not used
yet, but will be used in the next patch.

Co-Authored-By: Tom de Vries <tdevries@suse.de>