Add EvenDimmer to a11y settings page

- Add even dimmer to a11y settings page
- Additionally, use original extra dim icon next to setting to keep
  consistency with the rest of the a11y settings. This is the only
  difference from the setting in settings > Display.

Bug: 336476699
Test: manual
Change-Id: I5c0cb25f2ae61560346d3f051fe5dfec0e404739