Call view: minor improvements

**Is your feature request related to a problem? Please describe.**
In call view, I feel some information are missing and would be nice to have it.

**Describe the solution you'd like**
1/ The participants number is not there/ not visible.
2/ When someone is screensharing, I don't see who is that participant. It will be good to see their name at the bottom like in web
3/ The close screenshare button seems not aligned with the shape of the share stream (e.g: sharing a desktop screen , the rectangle is too far from the close button so they sometimes seem unrelated). If it is closer and aware of the shape or add a light frame to indicate that's an overlay, that will look better.

**Describe alternatives you've considered**
Mentioned above