libziparchive: start moving to a non-ZipString StartIteration API.

Same issue as with FindEntry: using ZipString in the API forces all
callers to make sure they don't hit the ZipString length limits. Switch
to std::string_view and uniformly use the empty string as a way to
signal no prefix/suffix rather than nullptr.

Also use default arguments to make the common case of no prefix and no
suffix more convenient.

Also just use std::string to increase the lifetime of the provided
prefix/suffix rather than manual memory management.

Bug: http://b/129068177
Test: treehugger
Change-Id: I6675e39ce62fadd766386d77d27423013c17d6f7