There are some situations where we want to work with a type-name-wrapped
dict that includes the type information, and others where we don't want
that. The main reason is that nested IEs can only be reconstructed if
we can determine the type/class of the nested IE from the dict data.
Let's explicitly offer {to,from}_val_dict() methods that work with
the value-part only
Related: OS#6453
Change-Id: I81654ea54aed9e598943f41a26a57dcc3a7f10c2