Implement JSON_SCHEMA_VALIDATION_REPORT()

Implement JSON_SCHEMA_VALIDATION_REPORT(schema, document) in MariaDB, following MySQL 8.0 behavior as closely as practical.

The function should return

on success, and on failure return a JSON object with fields such as valid, reason, schema-location, document-location, and schema-failed-keyword.

The function is based on MySQL 8.0's existing implementation. For MySQL compatibility, the relevant schema-validation standard is JSON Schema Draft 4.