Let user be able to export comments along with .fig file

There is currently no place for Qt Bridge for Figma users to input comments. "Properties" can only accept property: value pair. Snippet can only accept Component. A plain comment is nowhere to go.

Sometimes, people may need to add some for, e.g., copyright info or whatever description they want programmer to know. It can come in handy to have it in Bridge rather than modifying QML file.