Clarify ISO mdoc Handover structure.

[davidz25]

Fixes #415.

[c2bo]

Would it make sense to introduce tstr and bstr briefly as Major Type 2/3 with a reference to the CBOR spec? That reference to the Major Type 3 definition would also make it pretty clear that tstr must be UTF-8 encoded.

I would also assume that not all readers of this spec will be that familiar with CBOR and CDDL - an explicit reference might help.

[Sakurann]

+1 to two things Christian is suggesting (introduce tstr and bstr and references) as it is very true that the audience of this spec cannot be assumed to be cbor experts

[c2bo]

As mentioned, I think this section would benefit from introducing and referencing the CBOR types, but we could also do that in another PR.

I think the proposed changes to clarify the hashing are quite helpful.

[c2bo]

Suggested change

	* The second element MUST be a bytestring which contains the sha-256 hash of the bytes of `OpenID4VPDCAPIHandoverInfo` when encoded as CBOR.
	* The second element MUST be a byte string which contains the sha-256 hash of the bytes of `OpenID4VPDCAPIHandoverInfo` when encoded as CBOR.

[jogu]

Looks good, thanks David! I think further changes are necessary (clarifying effective client id, adding examples) but there are other issues open for that so it would be good to get this merged so the other issues can be worked on.