Update aod colors to ensure contrast

Especially if a dark custom color is chosen, the clock would not
be visible on AOD. Use system accent 100 to ensure contrast.

Fixes: 409526792
Test: atest DefaultClockProviderTest
Flag: com.android.systemui.shared.ambient_aod
Change-Id: I681c8e76fd0751f9ff1bf10bd5778ca33e29df5b