Check Zstandard implementation against changes to the spec

[dweiller]

A few issues we found while implementing the ZStandard decoder may result in minor updates to the zstandard spec - facebook/zstd#3508 is the main upstream issue that will hopefully link to any related changes that get made.

To close this issue it may best that the linked upstream issue is also closed, so that we know any spec-related issues have been resolved. Alternatively, this issue could be closed when the list below is addressed as we may need to periodically check for upstream spec changes unrelated to the issue linked above.

As of March 2024 these are changes that have been made in the reference Zstandard repo that require double checking our implementation:

• documentation changes in Clarify zstd specification for Huffman blocks facebook/zstd#3514

Extracted from #14702.