'1-1 call from anywhere' follow-ups

[Antreesy]

• Ref 📍 Call from anywhere - Integration of calls into the avatar menu #15416
• Follow-up to feat(call): start 1-1 call from anywhere #17205

Must for MVP:

• unlock integration in Files sidebar
  • webrtc/signaling cleanup should not mess with other integrations
  • allow to join if file conversation wasn't joined from Sidebar
  • need to initialize OCA.Talk later, not when tab is mounted
• check z-index with Viewer / Text / Office / other integrations
• draggable cursor adjust

Nice to have:

• re-establishing call after navigation / page-reload, if wasn't explcitly left
• minimize / increase size
• open 'call to' in new tab always
• should close the integration, if call joined from a full app
• Contacts app - add new action

Technical debt:

• clean up integrations UI
• clean up integration logic (reduce size, remove redundant code)
• delegate more to async loading
• test with another talk instance up

Not relevant, for discussion:

• chat integration?
• join calls from notifications
• join / start group calls?