feat(GuildEmoji): cache the author (#4334)

Co-authored-by: Papaia <43409674+Papaia@users.noreply.github.com>

typings/index.d.ts

@@ -793,6 +793,7 @@ declare module 'discord.js' {
   export class GuildEmoji extends BaseGuildEmoji {
     public readonly deletable: boolean;
     public guild: Guild;
+    public author: User | null;
     public readonly roles: GuildEmojiRoleManager;
     public readonly url: string;
     public delete(reason?: string): Promise<GuildEmoji>;