Microphone: buttons in pressed state don't update their state

[dstorey]

https://developer.microsoft.com/en-us/microsoft-edge/testdrive/demos/microphone/

Pressed state is visually changed by adding a class. It needs to inform the accessibility tree that the state has changed to the pressed state. I believe (off the top of my head) this should use the aria-pressed attribute, but double check before fixing it.