Minor resource cleanup for A11yMenu.

- Adds `supportsRtl`, matching AAS version.
- Uses string resource for app name
- Fixes app icon to use adaptive icon
- Adds sw600dp intro images, copied from AAS version.
- Adds javadocs to adjustBrightness() mentioning SysUI slider

Bug: 261252772
Test: inspect modified resources on device
Change-Id: Ibb47b7bfbf88e727f2dfdaaeb9e8f9e6c5602886