Implement compareStrictly() using phone_number_compare() written in C.

As per several discussions, we stick to the default behavior now.
In stead, we provide compareStrictly() as a hidden method, so that some
internal components are able to use the method if needed.

Since these are static methods, they cannot refer to the configuration files,
whose values can be obtained only via Resources object.

Please make callers' side if you want to use strict version of compare().

Internal issue number: 1892808