Parity for Collaboration

### What

We should have the same behavior across clients for collaboration, i.e. by utilizing the Collaboration panel to invite collaborators instead of adding email addresses in the tags section.

### Why

Currently, all the other apps have a dedicated Collaboration panel. In the Mac app, tapping the Collaborate item in the Actions menu displayed a tooltip to add an email address as a tag.


Start by tracing the Actions menu's Collaborate item, the Collaboration panel, and the tags section in the macOS client; the issue names no files or tests. Compare the collaboration behavior in the other clients, then verify that Collaborate opens the dedicated panel for inviting collaborators rather than directing users to add email addresses as tags.

Written by the indexing model from the issue text.