Disable volume dialog slider when the stream is zen muted

This brings back usage of the ColorStateList for the track, thumb and
icons colors, which doesn't work great with the dark/light theme
switching. This will be addressed in a follow up CL.

Flag: com.android.systemui.volume_redesign
Bug: 369994956
Test: manual on the phone. Open volume dialog with current stream being
disabled by the zenmode.

Change-Id: I0d3eddf1630a7559af48913a699c183f0ec280db