Migrate from `GZipFile`/`Tar` to `\PharData`

[dtdesign]

Our tar implementation supports GNU tar only and suffers from the bad handling of other POSIX standards, notably, pax. Extracting a pax archive will yield a lot of PaxHeaders files that are meta data and not actual files.

The \PharData class is the base implementation that phar archives are based upon.

However, it depends on the phar extension and zlib (for gzip compression), so it is unclear if we can actually use it.