Replace usages of ShortNumberUtil with ShortNumberInfo

The ShortNumberInfo class appears to support the exact same
methods as the ShortNumberUtil class (at least in terms of the
methods used by this project) but is a singleton and so
instances cannot be created directly but instead must be
retrieved using the static getInstance() method.

The ShortNumberUtil class was deprecated in version 5.8 and
removed in 7.2.3 of libphonenumber. This change is required in
order to allow libphonenumber to be upgraded to 7.2.4.

Bug: 26975810
Change-Id: Ide40c65d12cb44453f84600fc4b5ad1ee1088470