[MM-55153] Consolidate Desktop App API, use new contextBridge endpoints when available (#25438)

* Create Desktop API module, migrate message passing code

* Changes to use new API

* Use Desktop API to notify when mentions/unreads/expired changes

* Expose Desktop App module to plugins

* Fix lint

* PR feedback

* Fixed an issue where I forgot to check if the method exists first

* Slight API changes

* Fix package

* Convert all to class, add comments, small reworks for PR feedback

webapp/channels/package.json

@@ -14,6 +14,7 @@
     "@mattermost/client": "*",
     "@mattermost/compass-components": "^0.2.12",
     "@mattermost/compass-icons": "0.1.39",
+    "@mattermost/desktop-api": "5.7.0-1",
     "@mattermost/types": "*",
     "@mui/base": "5.0.0-alpha.127",
     "@mui/material": "5.11.16",