Add ZWSP when federating emojis for Mastodon compatibility (#5810)

* Add ZWSP when federating emojis for Mastodon compatibility

* Use unicode escape sequence

src/mfm/toHtml.ts

@@ -87,7 +87,7 @@ export function toHtml(tokens: MfmForest | null, mentionedRemoteUsers: IMentione
 		},
 
 		emoji(token) {
-			return doc.createTextNode(token.node.props.emoji ? token.node.props.emoji : `:${token.node.props.name}:`);
+			return doc.createTextNode(token.node.props.emoji ? token.node.props.emoji : `\u200B:${token.node.props.name}:\u200B`);
 		},
 
 		hashtag(token) {