[Expressive Design] Update color logic in BannerMessage

- Button Color should change if attention level updated.
- Flip text color of negative btn under attention level MEDIUM for contrast
- Fix some test failure.

Bug: 397336535
Bug: 359066481
Test: atest BannerMessagePreferenceTest
Flag: com.android.settingslib.widget.theme.flags.is_expressive_design_enabled
Change-Id: I9d2a76d2daa427ecb9c0fd2cb80d240fd6941097