feat: add emoji argument

This should be merged alongside sapphiredev/framework#349

docs/Guide/arguments/built-in-arguments.mdx

@@ -23,6 +23,7 @@ To facilitate creating commands and getting your bot running, Sapphire bundles a
 - `date`: Resolves to a [`Date`][date] instance, given a valid date format. For a list of valid date formats see
   [Several ways to create a Date object on MDN][mdn-date]
 - `dmChannel`: Resolves to a [`DMChannel`][dmchannel] instance, given a DM channel ID or user's ID.
+- `emoji`: Resolves to an [`EmojiObject`][emojiobject]. The `id` is `null` for Twemojis.
 - `float` / `number`: Resolves to any number.
 - `guildCategoryChannel`: Resolves to a [`CategoryChannel`][categorychannel] instance, given a category channel name,
   mention or ID.
@@ -52,13 +53,17 @@ To facilitate creating commands and getting your bot running, Sapphire bundles a
 - `enum`: Resolves to a string if it occurs within the [`array`][array] of possible items that is passed as an option
   (`enum`).
 
+[array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
 [boolean]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean
 [categorychannel]: https://discord.js.org/#/docs/main/stable/class/CategoryChannel
 [channel]: https://discord.js.org/#/docs/main/stable/class/Channel
 [date]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
 [dmchannel]: https://discord.js.org/#/docs/main/stable/class/DMChannel
 [guildchannel]: https://discord.js.org/#/docs/main/stable/class/GuildChannel
+[emojiobject]: ../../Documentation/api-framework/interfaces/Resolvers.EmojiObject
 [guildmember]: https://discord.js.org/#/docs/main/stable/class/GuildMember
+[mdn-date]:
+  https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#several_ways_to_create_a_date_object
 [message]: https://discord.js.org/#/docs/main/stable/class/Message
 [newschannel]: https://discord.js.org/#/docs/main/stable/class/NewsChannel
 [role]: https://discord.js.org/#/docs/main/stable/class/Role
@@ -68,6 +73,3 @@ To facilitate creating commands and getting your bot running, Sapphire bundles a
 [url]: https://nodejs.org/api/url.html
 [user]: https://discord.js.org/#/docs/main/stable/class/User
 [voicechannel]: https://discord.js.org/#/docs/main/stable/class/VoiceChannel
-[mdn-date]:
-  https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#several_ways_to_create_a_date_object
-[array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array