src/vs/editor/contrib/linesOperations/browser/linesOperations.ts/SnakeCaseAction/_modifyText
class SnakeCaseAction:	protected _modifyText(text: string, wordSeparators: string): string {
		const caseBoundary = SnakeCaseAction.caseBoundary.get();
		const singleLetters = SnakeCaseAction.singleLetters.get();
		if (!caseBoundary || !singleLetters) {
			// cannot support this
			return text;
		}
		return (text
			.replace(caseBoundary, '$1_$2')
			.replace(singleLetters, '$1_$2$3')
			.toLocaleLowerCase()
		);
	}