fix: Chat.isMuted (#2999)

* fix: isMuted returns true or false

* docs: add missing parts

* refactor: apply simplification

* fix: update chat instance after calling mute/unmute

* stylee: clarify and fix docs

* fix: fix convertation of Date to timestamp

* refactor: small code refactor

src/util/Injected/Utils.js

@@ -461,7 +461,7 @@ exports.LoadUtils = () => {
         let res = chat.serialize();
         res.isGroup = false;
         res.formattedTitle = chat.formattedTitle;
-        res.isMuted = chat.muteExpiration == 0 ? false : true;
+        res.isMuted = chat.mute?.expiration !== 0;
 
         if (chat.groupMetadata) {
             res.isGroup = true;