PLT-3980 sort custom emoji alphabetically by id. (#3893)

This sorts the emoji based on their id in the custom emoji list.

webapp/stores/emoji_store.jsx

@@ -56,6 +56,7 @@ class EmojiStore extends EventEmitter {
             this.addCustomEmoji(emoji);
         }
 
+        this.sortCustomEmojis();
         this.updateEmojiMap();
     }
 
@@ -76,6 +77,10 @@ class EmojiStore extends EventEmitter {
         this.updateEmojiMap();
     }
 
+    sortCustomEmojis() {
+        this.customEmojis = new Map([...this.customEmojis.entries()].sort((a, b) => a[0].localeCompare(b[0])));
+    }
+
     updateEmojiMap() {
         // add custom emojis to the map first so that they can't override system ones
         this.emojis = new Map([...this.customEmojis, ...this.systemEmojis]);