Add definition for zip64 struct

Add the definition of zip64 related structs. Also add place holders in
the zip parsing code. In addition, this cl changes the variable type of
num of entries to uint64_t. The number was capped at UINT16_MAX in zip32
format.

Bug: 150900468
Test: unit tests pass
Change-Id: I51a39e7b993fa376e0d050a04b8d39abae8a9e15