String readAll() {
            final String read = path.substring(index);
            index = path.length();
            return read;
        }
Parses 'Variable' part.

<p>
Variable = "{" FieldPath [ "=" Segments ] "}"
</p>
grpc/src/main/java/com/linecorp/armeria/server/grpc/HttpJsonTranscodingPathParser.java