Previously, dragging it all the way to the left would *not* mute the participant but rather bottom out at 10% volume, and people have found this unintuitive. Let's make it less silly by giving the slider a range of 0% to 100%, and making the mute toggle button have the same effect as dragging the slider to zero. When unmuting, it will reset to the last non-zero "committed" volume, similar to how the volume sliders in desktop environments work.
Catching two accessibility issues along the way: we were putting the wrong accessible labels on the 'expand' button, and even the off-screen pages of the spotlight tile were being exposed to accessibility technologies rather than hidden.
This was the result of me playing around with RxJS marble testing to understand how to get things done with its TestScheduler. I discovered that it lacks a clear way to fire arbitrary actions during the test, so I built a small helper function called schedule which does this for us.
