hacks: support symbolic links in .zip files

Add support for re-creating symbolic links when unpacking .zip files, copying the complete implementation of ZipFile._extract_member() and adding the needed modifications. As a safeguard to avoid following symlinks when re-unpacking the same file, which could result in wrong output, always unlink each destination file before creating it.

Issue originally reported at https://github.com/Igalia/wpe-android/issues/50