feat(expressive): Replace a11y SeekBar prefs with Slider prefs.

Fix: 375168747
Test: atest com.android.settings.accessibility
Test: observe new sliders and their interaction with the preview;
      see attachments in bug
Test: use TalkBack to interact with sliders; observe state is announced
Flag: EXEMPT refactoring with user-visible differences only visible
      when the Settings expressive flag is enabled
Change-Id: I5b92bc3b06b591ee23f5631b9829148b8714159e