[MessageBarGroup] Migrate to Fade motion component

[robertpenner]

MessageBarGroup uses Griffel animationName for opacity transitions:

// useMessageBarGroupStyles.styles.ts
enter: {
  animationName: {
    from: {
      opacity: 0,
      transform: 'translateY(-100%)',
    },
    to: {
      opacity: 1,
      transform: 'translateY(0)',
    },
  },
},

exit: {
  animationName: {
    from: {
      opacity: 1,
    },
    to: {
      opacity: 0,
    },
  },
},

Replace the opacity CSS keyframes with a Fade motion component.

[robertpenner]

Pausing to investigate migration of fade + slide together.

[layershifter]

Closing as a dupe as there is #33470.