Rename GeoTimeZoneFinderImpl to S2RangeFileBasedGeoTimeZoneFinder.

Also make it package-private and mark fileReader field as
NonNull.
Left GeoTimeZoneFinder.create method untouched.

Bug: 152746105
Test: presubmit only.

Change-Id: I1dbf64687f57bbc26e5e98300fa6117124381fb2
3 files changed