Improve code readability on some functions

[TheLiux]

Hi!
While I was checking the code, I noticed some functions with nested if that caught my attention.

Example:

Color _getSwitchThumbColor(Set<MaterialState> states, ColorScheme colorScheme) {
  if (states.contains(MaterialState.disabled)) {
    if (states.contains(MaterialState.selected)) {
      return colorScheme.onSurface.withOpacity(0.5);
    }
    return colorScheme.onSurface.withOpacity(0.5);
  } else {
    return colorScheme.onPrimary;
  }
}

Honestly, if is not necessary, I find nested if like this confusing when i read the code.
I think a better approach like this with early returns is better than the current:

Color _getSwitchThumbColor(Set<MaterialState> states, ColorScheme colorScheme) {
  if (states.contains(MaterialState.disabled)) {
    return colorScheme.onSurface.withOpacity(0.5);
  }

  return colorScheme.onPrimary;
}