Change Issued JWK / Presented JWK Protected Headers

[dwaite]

New headers instead describe Issued/Presented Keys as part of CBOR addition.

This resulted in a slightly larger change with some additional editorial cleanups.

1. The Proof Key and Presented Key definitions were in JWP, while the registry was in JPA. Moved the registry to JWP.
2. The text was simplified by referring to e.g. "Proof Key protected header" rather than "the proof_key issuer protected header value"
3. Requirements and usage purpose information inline in the algorithms leveraging these header parameters were moved to JWP under the header definitions.
4. There was clarification in the new definition that the header parameters are not mandatory in general (specific algorithms mandate them).