Instead of manually updating emoji.txt whenever new emoji are added,
we use Unicode's emoji-test.txt to generate emoji.txt on each build,
including only the emojis that Serenity supports at that time.
By using emoji-test.txt, we can also include all forms of each emoji
(fully-qualified, minimally-qualified, and unqualified) which can be
helpful when double-checking how certain forms are handled.
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