Tweak tzdata format

Add a new placeholder pointer that signifies the end of the zone.tab
section of the file. This will enable us to easily add sections in the
future if we want to. It also lays the groundwork for removal of
zone.tab from the file.

Test: atest CtsIcuTestCases
Bug: 161699306
Change-Id: I01bb0fb4b7357ada7763848cfeb728c1267edd84
2 files changed