Add an emote preview when you're uploading an emote

[ornate rose]

When you upload an emote, show the way the emote will look in chat in both dark and light modes, like on the emote testing websites

[scenic patio]

#1011557624044584971 message

[swift ibex]

why was this never implemented

can you make a pr again

[nimble merlin]

if we're gonna implement this put file requirements and fix the private/zero-width options while you're at it