(live) improve UX for document sharing

[NamFra]

Bug Report

Problematic Behavior
The SharedLiveMedia widget has been redesigned, and document sharing and download permissions are now presented more explicitly.

Then

It was necessary to first Stop sharing the current document to display another one (option grayed out).

Now

It is now possible to activate the switch for another document while another document is currently being shared.

Expected behavior/code
Using the switch on another document should disable the active document without generating an error.

Steps to Reproduce

1. Create a webinar
2. Add 2 files using the document sharing widget
3. Activate the share support switch on one document
4. Activate the switch on the other document without deactivating the first one
5. See the error 'Share media update has failed !'"

Environment

• Marsha version: Staging

Additional context/Screenshots
https://github.com/openfun/marsha/blob/master/src/frontend/packages/lib_video/src/components/common/VideoWidgetProvider/widgets/SharedLiveMedia/index.spec.tsx

live-shared-media-failed.webm