src/vs/editor/contrib/linesOperations/linesOperations.ts/SnakeCaseAction/_modifyText
class SnakeCaseAction:	protected _modifyText(text: string, wordSeparators: string): string {
		const regExp1 = SnakeCaseAction.regExp1.get();
		const regExp2 = SnakeCaseAction.regExp2.get();
		if (!regExp1 || !regExp2) {
			// cannot support this
			return text;
		}
		return (text
			.replace(regExp1, '$1_$2')
			.replace(regExp2, '$1_$2$3')
			.toLocaleLowerCase()
		);
	}