Fundamentally this `.Print()` is wrong for debug output at present because `.fixed_spelling()` can be empty. It's also inconsistent with other enums to use it. We frequently print tokens for debugging, and it's easy to forget to specify `.name()` there.
Diagnostics use formatv, so we can provide a format_provider and address it in one spot that way. It also makes it harder to just forget to do the right thing.