TimeZoneDistroInstaller changes + knock-ons

This change modifies TimeZoneDistroInstaller so it stages
operations to be applied to the active/current time zone
data directory rather than performing them immediately.

This ensures that a time zone data update cannot go live
partially and it is clear what time zone rules are in use
on device.

There are associated changes in system/core to the tzdatacheck
binary to perform the "commit".

Test: Manual testing
Test: CTS: Ran libcore.tzdata.share2 and libcore.tzdata.update2 tests
Bug: 31008728
Change-Id: I22573268e6e6be071d30f12a7f7ee9528dca8737