src/vs/editor/common/languages/supports/tokenization.ts/ThemeTrieElement/toExternalThemeTrieElement
class ThemeTrieElement:	public toExternalThemeTrieElement(): ExternalThemeTrieElement {
		const children = new Map<string, ExternalThemeTrieElement>();
		this._children.forEach((element, index) => {
			children.set(index, element.toExternalThemeTrieElement());
		});
		return new ExternalThemeTrieElement(this._mainRule, children);
	}