Add DSLX Zstandard Codec

This is an umbrella issue to track the implementation of the DSLX Zstandard Decoder and Encoder.

The created modules should be compatible with [RFC8878](https://datatracker.ietf.org/doc/html/rfc8878). The encoder, when fed with data should provide an output encoded in Zstandard format. The same data decompressed with the original [zstd library](https://github.com/facebook/zstd) should restore the data to its initial form. Similarly, the created decoder should be able to decompress data encoded in Zstandard format and provide the original data on its output (if the memory requirements necessary for decompressing the stream are fulfilled by the decoder).

Here is a list of opened PRs related to this issue:
* https://github.com/google/xls/pull/1166
* https://github.com/google/xls/pull/1167
* https://github.com/google/xls/pull/1168
* https://github.com/google/xls/pull/1212
* https://github.com/google/xls/pull/1213
* https://github.com/google/xls/pull/1214
* https://github.com/google/xls/pull/1169

CC @proppy