Bring back waveform for voice messages and retain seeking (#8843)

* Crude way of layering the waveform and seek bar

Not intended for production.

* Use a layout prop instead of something less descriptive

* Fix alignment properly, and play with styles

* Convert back to a ball

* Use `transparent` which makes NVDA happy enough

* Allow keyboards in the seek bar

* Try to make the clock behave more correctly with screen readers

MIDNIGHT

* Remove legacy export

* Remove redundant attr

* Appease the linter

src/components/views/audio_messages/PlaybackClock.tsx

@@ -76,7 +76,7 @@ export default class PlaybackClock extends React.PureComponent<IProps, IState> {
         }
         return <Clock
             seconds={seconds}
-            aria-live={this.state.playbackPhase === PlaybackState.Playing ? "off" : undefined}
+            role="timer"
         />;
     }
 }