[Glitch] Modern Emoji: Use local storage to opt-in

Port b81670776fd757341f5ec9060b6341ec2b23af63 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/utils/environment.ts

@@ -19,5 +19,12 @@ export function isFeatureEnabled(feature: Features) {
 }
 
 export function isModernEmojiEnabled() {
-  return isFeatureEnabled('modern_emojis') && isDevelopment();
+  try {
+    return (
+      isFeatureEnabled('modern_emojis') &&
+      localStorage.getItem('experiments')?.split(',').includes('modern_emojis')
+    );
+  } catch {
+    return false;
+  }
 }