Refactored `supportsUniqueKey` function to a common implementation in `CommonProcessInterface` to eliminate duplicate code across MongoDB process interfaces.

The function now takes an `IndexDescriptor` and collator parameters instead of working with raw BSONObj index definitions, providing a more consistent interface for checking if an index supports unique keys.

This change consolidates the logic that was previously duplicated in `mongodb_process_interface.cpp`, `common_mongod_process_interface.cpp`, and `mongos_process_interface.cpp`.