Ensure theme name is used as key instead of isDark where appropriate

[rock3r]

In the bridge, it's technically wrong to use isDark as remember key because the user may be switching between two different themes that are both light, or dark. E.g., Dark -> Darcula.

So the next step after #353 is to review usages of isDark as remember key, and replace them with the theme name, to avoid missing recompositions in the bridge.

This is only really a problem for the bridge, since in standalone you only have light or dark.