Update TzLookupGenerator tool to use a fixed time

Update TzLookupGenerator tool to use a fixed time when
validating offsets in the country_zones.txt file.

The output file is not affected - it just affects
whether the generation fails. Mismatched offsets
suggest the country_zones.txt ordering has not been
reassessed after the time zone's offset changed.

Bug: 69842297
Test: Ran tool with the corrected country_zones.txt
Test: Ran unit tests as per README.android
Change-Id: Id0e78e4d5290db5c0c412219d7b87b971376c80a