Import ZStandard v1.4.5

ZStandard is a modern, high performance, general compression algorithm.
It provides similar or better compression levels to GZIP, but with much
better performance. ZStandard provides a large selection of compression
levels to allow a storage administrator to select the preferred
performance/compression trade-off.

This commit imports the unmodified ZStandard single-file library which
will be used by ZFS.

The implementation of this new library is done with future updates of
zstd in mind. For this reason we integrated the code in a way, that does
not require modifications to the library. For more details, see
module/zstd/README.md.

The library is excluded from codecov calculation and cppcheck as
unaltered dependencies do not need full codecov or cppcheck.

Co-authored-by: Allan Jude <allanjude@freebsd.org>
Co-authored-by: Kjeld Schouten-Lebbing <kjeld@schouten-lebbing.nl>
Co-authored-by: Michael Niewöhner <foss@mniewoehner.de>
Signed-off-by: Allan Jude <allanjude@freebsd.org>
Signed-off-by: Kjeld Schouten-Lebbing <kjeld@schouten-lebbing.nl>
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>