Leave call when closing files sidebar

Steps to reproduce

1. Share a file with other people
2. Start a call in the sidebar for that file
3. Close the sidebar
4. Redo the steps but this time switch to another file during the call.

Expected behaviour

A warning appears, telling me that I'm about to leave the call.
If I accept, the call ends and context is switched.
Otherwise the sidebar stays open.

Actual behaviour

The sidebar closes, the call is ongoing.
If I click on other files, somehow it seems the chat window is still the one from the current file (might be another bug).
There is a risk that I get lose in other folders and don't remember where the call is happening.

In the files app the context can be switched to another file, so to me it makes sense to end the call.
However, if a file is currently open (ex: office doc or markdown), then closing the sidebar should not end the call but maybe an indicator should be shown somewhere that a call is ongoing.

Talk app

Talk app version: 11.0.0-dev.2 (from git master)

Start by reproducing the call, sidebar-close, and file-switch flows in the Files app with the Talk sidebar. Trace the existing handling for closing the sidebar and switching file context, then verify the warning, call termination, context switch, and ongoing-call indication described in the expected behavior.