Update material-yes-no-buttons mixins to use CSS shimming.
Update material-yes-no-buttons mixins to use CSS shimming.

Unfortunately, despite the warning at the top of the file, unique selectors
were not used (witness selectors such as '', '.buttons', or '.yes-no-buttons'),
causing mixins to override other mixins in other parts of the app or even in
other apps entirely. This is especially problematic when a mixin overrides the
button text color to be the same as the background color, effectively making
the button invisible.

PiperOrigin-RevId: 173286018

angulardart/angular_components,angulardart/angular_components,angulardart/angular_components