Legacy Unit Page UI: Update tag counts when changes are saved in the tag drawer

[bradenmacdonald]

1. In the edx-platform legacy UI, when the user makes changes to the tags of a component or unit, the tag counts (green) should be updated automatically.
   
2. On the legacy outline page, if the user uses the "Manage Tags" menu to change the tags of a Unit, the tag count should also be updated automatically.

[bradenmacdonald]

Note there are two existing WIP PRs for this, but they need major rebasing as the code has changed signfiicantly:

• refactor: Update tags drawer listener for a Json message openedx-platform#34223
• feat: Send message after update tags on content [FC-0036] frontend-app-authoring#800