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
diff --git a/libziparchive/unzip.cpp b/libziparchive/unzip.cpp
index c6def73..3a3a694 100644
--- a/libziparchive/unzip.cpp
+++ b/libziparchive/unzip.cpp
@@ -249,7 +249,7 @@
   // libziparchive iteration order doesn't match the central directory.
   // We could sort, but that would cost extra and wouldn't match either.
   void* cookie;
-  int err = StartIteration(zah, &cookie, nullptr, nullptr);
+  int err = StartIteration(zah, &cookie);
   if (err != 0) {
     error(1, 0, "couldn't iterate %s: %s", archive_name, ErrorCodeString(err));
   }