2025 spec: increase inverse on surface contrast

[KTibow]

2025 inverse on surface is frankly gray
light theme:

dark theme:

the result is a contrast-wise regression from the 2021 spec. look how little contrast it has when being used as a disabled slider's ticks:

and how hard to read this light mode snackbar is:

fix: increase contrast levels to at least typical "on surface" levels

[deminearchiver]

Android 16 QPR1 (the version that introduced support for Material 3 Expressive and the 2025 color spec for Dynamic Color) doesn't seem to use the inverse-surface role at all. Instead, it takes the surface and on-surface colors from the inverse mode (dark for light and light for dark). This makes inverse-on-surface have more contrast. I suggest implementing this behavior as a temporary workaround.