C2PA-272: Final 1.4 spec C2PA table - add reserved field

[chriskushmonotype]

Changes in this pull request

(Integrate upstream changes), and then update the rust-font-tools reference to get support for the two-byte reserved field added in the final 1.4 C2PA table specification.

The upstream merge depends on a earlier PR for Monotype/c2pa-rs.

Checklist

• [ ] This PR represents a single feature, fix, or change.
• [ ] All applicable changes have been documented.
• [ ] Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment.