Responding to Volume slider changes in discrete steps for haptics.

Calls to the haptics view-model are not performed only on discrete step
changes of the animated slider value. The previous discrete step is also
remembered to avoid calling haptics for the same stepped value.

Test: manual. Verified haptics are played for every discrete step
  changed of the sliders in the volume panel.
Flag: com.android.systemui.haptics_for_compose_sliders
Bug: 382081935

Change-Id: I3cb27d91701b3def3e39f1c083c7bbe5275b4b81