fix(watermarks): bring watermarks to the top

[joshuai96]

The z-index of the PremeetingScreen is 252 while the watermarks only have the z-index of 2 or 100 for the "powered by". This hides the watermarks behind the content panel.

If the watermarks are hidden by design here, they should be conditionally excluded from the DOM, as they can be navigated to via keyboard. This breaks the sequential navigation required for accessibility.

I opted to bring the Watermarks to the top, as determining which view is currently active (prejoin, lobby or active conference) and bringing this information down to Watermarks (Conference -> LargeVideo -> Watermarks) seems a lot more hassle, but can be implemented that way, too.