Fix emoji exploit (#640)

## Description:
This should fix the exploit that allows players to send custom text as
an "emoji". It does this by introducing a emoji ID (index into the emoji
table) instead of sending the raw emoji as a string.

## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [X] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [X] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:
PilkeySEK

src/core/execution/EmojiExecution.ts

@@ -7,6 +7,7 @@ import {
   PlayerID,
   PlayerType,
 } from "../game/Game";
+import { flattenedEmojiTable } from "../Util";
 
 export class EmojiExecution implements Execution {
   private requestor: Player;
@@ -17,7 +18,7 @@ export class EmojiExecution implements Execution {
   constructor(
     private senderID: PlayerID,
     private recipientID: PlayerID | typeof AllPlayers,
-    private emoji: string,
+    private emoji: number,
   ) {}
 
   init(mg: Game, ticks: number): void {
@@ -38,10 +39,12 @@ export class EmojiExecution implements Execution {
   }
 
   tick(ticks: number): void {
+    const emojiString = flattenedEmojiTable.at(this.emoji);
+
     if (this.requestor.canSendEmoji(this.recipient)) {
-      this.requestor.sendEmoji(this.recipient, this.emoji);
+      this.requestor.sendEmoji(this.recipient, emojiString);
       if (
-        this.emoji == "🖕" &&
+        emojiString == "🖕" &&
         this.recipient != AllPlayers &&
         this.recipient.type() == PlayerType.FakeHuman
       ) {