registerIconCollectionForTheme = (collectionName, themeCollectionMap) => {
    if (iconCollections.has(collectionName)) {
      iconCollections.set(collectionName, {
        ...themeCollectionMap,
        ...iconCollections.get(collectionName)
      });
      return;
    }
    iconCollections.set(collectionName, themeCollectionMap);
  }
Registers collection version per theme.
</b>For exmaple:</b> registerIconCollectionForTheme("my-custom-icons", {"sap_horizon": "my-custom-icons-v5"})
@param { string } collectionName
@param { ThemeToCollectionMap } themeCollectionMap