Support emoji, or at least provide an error so they can be removed

[baumanj]

If a question contains an emoji, it appears that Moderator converts it to "???" without providing an error, leading to a confusing mutation to the content of a question. Ideally, emoji would be properly displayed, but failing that, an error which allows the user to revise the question would be preferable to the current behavior.

[clarmso]

I entered a ❤️ emoji in Moderator but Moderator renders as ?? as well.