public static Path resolveChildOf(Path root, String path) {
        Path resolved = root.resolve(path);
        validateChildOf(root, resolved);
        return resolved;
    }
Resolves a path under a root path
@param root root poth
@param path child to resolve
@return The resolved path
@throws IllegalArgumentException If the provided child path does not resolve as child of root
vespajlib/src/main/java/ai/vespa/validation/PathValidator.java