Their names must have come from a very old version of the app, they
both toggle the fullscreen mode and rotate the screen depending on
circumstances.
So
`fullscreenButton` -> `fullscreenToggleButtonSecondaryMenu` because it
is only visible in the secondary video menu on some configurations.
and
`screenRotationButton` -> `fullscreenToggleButton` because it is the main
fullscreen button next to the video progress bar.
753a3e68d5