libzipplugin: add support for zstd compression
PKWARE added zstd compression method to zip specification, originally was pushed and supported only by WinZip Pro.
Compression level limited by 9 (libzip limitation) but zstd itself supports up to 22 (without using --ultra methods) see https://github.com/nih-at/libzip/issues/214 but anyway it seems like ark doesn't support different compression levels for different compression methods either.
https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
93 - Zstandard (zstd) Compression