Switch mcc/mnc to String from int

Switch mcc/mnc types in telephony_lookup_proto_file.proto to String from
int and improve validation / tests. jackyu@ in telephony pointed out that
they prefer Strings as there can be leading zeros.

This change also fixes TelephonyLookupGeneratorTest, which I checked in
broken :-/

Bug: 143451294
Test: ./update-tzdata.py and confirm no changes
Test: atest telephonylookup_generator_tests
Change-Id: I10ad9f6084f818e8e0680a2ed538a4cd73348782
5 files changed