fix(chat): capture token mismatch when receiving chat messages

[Antreesy]

☑️ Resolves

• Ref chatBlocks follow-ups #15668
• Attempt to identify the cause of the issue
• See comment in the original issue:
  • chatStore->getMessagesList, chatStore->processChatBlocks, messagesStore->processMessage are storing and showing correctly to the arguments - given token and messages[]
  • That means some of functions is passing a new token with old messages to process*()
  • And open chat (with new token) might show 'old messages'
• WIth this PR:
  • Mismatching messages will be ignored and not saved. Page reload or another conversation switch should bring them back with the new request (if this one isn't failing too)

Tip

As it's tricky to reproduce with client only, easy way to mock it is to modify ChatController.php#prepareCommentsAsDataResponse():
Use <some_token> from a known conversation as an indicator - this conversation will work as expected

+		foreach ($messages as $idx => $message) {
+			$messages[$idx]['token'] = '<some_token>';
+		}
 		return new DataResponse($messages, Http::STATUS_OK, $headers);
 	}

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
  • Not risky to federations, as tokens are translated
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[Antreesy]

/backport to stable32