Slash commands accepting stickers as argument

[Maverick-Wolf]

As of now, slash commands just don't work with stickers, a user cannot even pass stickers as a string argument and allow us, developers, to parse the sticker out of it.
So I just request a new type of argument being introduced to slash commands which will accept emojis and stickers, or just allow stickers to be passed as string arguments in the slash commands.

[Skye-31]

Tagging on #3330 which was specifically for emojis, this should be included too