Gets the Atom that was used to create
When an Atom is provided during
construction, this may be a reference to an IndirectObject rather
than a direct reference to an Atom.
If this is the case then the reference needs to be resolved
through to an Atom.
The Ref property stores the RefAtom, if
one was provided. The Atom property
stores the resolved Atom.
This property will return the Ref if it
is not null, or the Atom if it is.