Avoiding an extra coroutine on continuous volume panel slider haptics.

Continuous slider haptics require a more responsive behavior and more
logic and computations. We can coptimize the overall UIs if we avoid
extra LaunchedEffects by calling the SliderHapticsViewModel on existing
coroutines that already respond to the slider value change.

Test: manual. Verified continuous haptics are delivered by volume panel
  sliders
Flag: NONE bugfix
Bug: 422308419
Change-Id: Ie312a565cd4da82da0bb8bc1f98960742eabefe7