mDL date fields are encoded as strings instead of dates

[juangj]

Using CMWallet with https://digital-credentials.dev/ to request org.iso.18013.5.1/birth_date, I see the birth date returned as a tstr (CBOR major type 3), but the mDL spec calls for a full-date (major type 6, tag 1004). The same issue occurs for org.iso.18013.5.1/expiry_date, which should be encoded as a tdate (tag 0) or a full-date (tag 1004), but is actually encoded as tstr.

This is the CBOR I receive for birth_date:

A4                                      # map(4)
   68                                   # text(8)
      6469676573744944                  # "digestID"
   04                                   # unsigned(4)
   66                                   # text(6)
      72616E646F6D                      # "random"
   50                                   # bytes(16)
      99C1F724A397436ACBF40C2D5BC90BF0  # "\x99\xC1\xF7$\xA3\x97Cj\xCB\xF4\f-[\xC9\v\xF0"
   71                                   # text(17)
      656C656D656E744964656E746966696572 # "elementIdentifier"
   6A                                   # text(10)
      62697274685F64617465              # "birth_date"
   6C                                   # text(12)
      656C656D656E7456616C7565          # "elementValue"
   6A                                   # text(10)
      313938382D30392D3031              # "1988-09-01"