simplifying signer behavior for corim / xcorim

[nedmsmith]

Given we want a generic signing tool to accept an unsigned CORIM (XCORIM) file and use it as the payload of COSE-Sign1 without having to understand that the global tags (e.g., #6.500 and #6.501) should be removed before signing. The schemas should be modified slightly to define a tagged-corim-map that contains the global tag that is used as the payload parameter to COSE_Sign_1.

e.g.,

tagged-corim-map = #6.501 (corim-map)
COSE-Sign1-corim = [
      protected: bstr .cbor protected-corim-header-map
      unprotected: unprotected-corim-header-map
      payload: bstr .cbor tagged-corim-map ; was corim-map
      signature: bstr
 ]

Additionally, the corim type choice should be updated to:

$concise-reference-integrity-manifest-type-choice /= tagged-corim-map