Create a new library encapsulating internet protocol related functions in core.

The need was identified while working on MDL-48498 and MDL-44467, in which domain name and IP address validation and matching was required for several things. Some functions existed within class.t3lib_div.php, however, these functions are untested and error prone in some cases.

After discussion, abgreeve and I decided we'd prefer not to further bloat moodlelib.php and instead we'd split out the library into a new issue, which would then block the aforementioned issues.