Decide if the form title should be mandatory

In web-forms the form will fail to load if it doesn't have a `` element.

https://github.com/getodk/web-forms/blob/6015ab6b3cb9ccc5b79ad4a453e95c6cae6c79f3/packages/scenario/test/label-hint-text.test.ts#L32-L34

This isn't a requirement in other implementations so either; decide whether it's something we still want to enforce and document the difference, or allow it and fix the code to handle it gracefully.

Start with packages/scenario/test/label-hint-text.test.ts around lines 32-34 and reproduce loading a form without a element. Determine whether the title should remain mandatory or be accepted, then document the cross-implementation behavior or verify graceful handling when the requirement is relaxed.

Written by the indexing model from the issue text.