Function expandThemeContribution

expandThemeContribution(
    themeFamiliesById: ThemeFamiliesById,
    defaultThemeFamily: undefined | ThemeFamily,
): {
    [key: string]:
        | undefined
        | {
            dark?: ThemeDefinitionExpanded;
            light?: ThemeDefinitionExpanded;
            [key: string]: undefined
            | ThemeDefinitionExpanded;
        };
}
Add the derived properties in ThemeDefinitionExpanded to ThemeDefinitions in the given ThemeFamiliesById and fill in any missing cssVariables in the theme definitions with those from the default themes.

Does not modify the input object.
Parameters
- themeFamiliesById: ThemeFamiliesById
  Theme families to expand with the additional derived properties
- defaultThemeFamily: undefined | ThemeFamily
  If provided, themes from this family are used to fill in missing cssVariables in the theme definitions to make sure each theme definition has all necessary cssVariables
Returns {
    [key: string]:
        | undefined
        | {
            dark?: ThemeDefinitionExpanded;
            light?: ThemeDefinitionExpanded;
            [key: string]: undefined
            | ThemeDefinitionExpanded;
        };
}
The expanded theme families
- Defined in lib/platform-bible-utils/src/theme.util.ts:68