src/vs/css.build.ts/CSSPluginUtilities/commonPrefix
class CSSPluginUtilities:	public static commonPrefix(str1: string, str2: string): string {
		const len = Math.min(str1.length, str2.length);
		for (let i = 0; i < len; i++) {
			if (str1.charCodeAt(i) !== str2.charCodeAt(i)) {
				return str1.substring(0, i);
			}
		}
		return str1.substring(0, len);
	}