The old VirtualMemoryTracker has a method set_reserved_region_type(address, flag). We implement this for the new VMATree implementation by altering the signature slightly to set_reserved_region_type(address, size, flag). This simplifies the implementation greatly for our new data structure and leads to trivial changes for the callers (all callers already know the size).

This ticket implements the internal implementation along with tests, but does not change any callers.