Emoji support not working exactly as intended.

[Tagl]

@gkreitz
I was trying to set up a statement that has both emojis in text and in the sample input.
With the current set up I got errors for both the standard font and the monospace font.

Missing character: There is no 🧦 (U+1F9E6) in font [lmmono10-regular]:!

I tried messing around a bit with the problemset.cls file and changed the font loading to the following which seems to work to support monospace fonts:

\IfFontExistsTF{NotoColorEmoji}{
    \directlua{luaotfload.add_fallback
    ("emojifallback",
    {
      "NotoColorEmoji:mode=harf;"
    }
    )}
}{}{}
\IfFontExistsTF{NotoColorEmoji}{
    \directlua{luaotfload.add_fallback
    ("mono_fallback",
    {
      "NotoColorEmoji:mode=harf;"
    }
    )}
}{}{}
\setmonofont{CMU TypeWriter Text}[
  NFSSFamily=Mono,
  RawFeature={fallback=mono_fallback}
]

\IfFontExistsTF{CMU Serif}{
    \setmainfont{CMU Serif}
}{}{}

Note, I have approximately 0% idea how this works, I'm just making arbitrary guesses here based on the limited information I find online.