TDML Runner hides warnings and validation errors

The TDML Runner currently hides warnings. This means that if we make a change that causes many new warnings it is very easy to not realize it.

Unfortunately, many tests, including those external to daffodil, might rely on this current behavior so we can't simply fail tests if warnings exist but there are no tdml:warnings in the TDML test.

However, we should at least have some mode that allows us to run the TDML runner and error if there are unchecked warnings. Or perhaps we always output warnings, which would encourage users to update their schemas or fix tests to suppress expected warnings. We could even provide a message that says in some future release uncheck warnings will always be considered an error if we want to go that route.