Introduce in-memory structure for tzlookup.xml

This commit introduces the CountryZonesFinder which
holds the entire contents of the <countryzones>
element from tzlookup.xml. It is intended for
usecases where the memory vs i/o trade off means
it's better to load the data once and keep it
pinned in memory. The pinning is left to the caller.

Bug: 63561146
Test: CTS: run cts -m CtsLibcoreTestCases
Change-Id: I36bb611149d8febc38f39db5a9c048c9549e1b1c
7 files changed