Add a toast to tell user disable self-view kept the webcam running

[antobinary]

Describe the bug
Notify (toast) the user that self-hide webcam does not mean the stream has stopped.

To Reproduce
Steps to reproduce the behavior:

1. Join a meeting
2. Share a webcam
3. Hit 'Disable self-view' in the webcam controls

Expected behavior
Let's show a toast to the user: 'Your webcam is still streaming even if self-view is disabled'.

Actual behavior
Some users are apparently not aware that the webcam is still streaming