Swift: Ensure A2UICommonSchema and schema JSON stay in sync

From this [PR comment](https://github.com/a2ui-project/a2ui/pull/1994/changes/BASE..d4e4f99ef04e85cc5dac1ecbfe27d9a72f72d046#r3600247088), it would be great if there was a way to generate the inline Swift representation of the core A2UI JSON schema so that they stay in sync. Ideally this could be done with code generation, but at the very least, there should be a way to enforce that they are the same in CI.