fix(concerto-vocabulary): look up terms by own property only

[apoorva-01]

Closes #1241

Vocabulary.getTerm and getElementTerms matched a property's term with propertyName in d, which walks the prototype chain. A property named after an Object.prototype member (hasOwnProperty, constructor, toString, valueOf) matched every declaration object and returned a built-in Function instead of the term, or a Function instead of null for an undeclared name.

Changes

• Both methods now use an own-property check, Object.prototype.hasOwnProperty.call(d, propertyName), so a term comes back only for a property actually declared on the object.
• Tests in test/vocabulary.js cover constructor/toString/hasOwnProperty resolving to their own terms and undeclared prototype names returning null; they fail on revert. Suite (95), lint and coverage green.

Flags

• Used hasOwnProperty.call rather than Object.hasOwn, which reads cleaner but isn't in the package's es2020 TS lib.
• Fixed getElementTerms alongside getTerm since it has the identical defect, happy to narrow to getTerm.
• Also covers the property-existence half of Vocabulary term lookups silently discard valid falsy values (empty string, null) #1183.

Related Issues

• Issue VocabularyManager.getTerm returns Object.prototype built-ins for property names that shadow Object.prototype (hasOwnProperty, constructor, toString, …) #1241
• Issue Vocabulary term lookups silently discard valid falsy values (empty string, null) #1183 (partly addressed)

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname