Refactoring to support an upcoming change

Making various changes to support a large
upcoming commit.

Most of the changes are in TzLookupGenerator
to split up a large method that is only
going to get larger.

Bug: 72142943
Test: Ran unit tests (see tzlookup_generator/README.android)
Test: Ran update-tzdata.py, tzlookup.xml had not changed
Change-Id: Ia10992c8f83eee9d619f77e4a18ecf8612f2e384