Add skip() to ZstdBufferDecompressingStream

[divijvaidya]

Users of ZstdBufferDecompressingStream may have a requirement to skip reading some uncompressed bytes. A similar method exists in ZstdInputStream.

The skip() method should:

1. Use a BufferPool if provided.
2. Allocate buffer only once from the BufferSupplier.
3. Returns the number of bytes skipped.

The interface should be modeled similar to InputStream#skip(long n).

[luben]

Sounds reasonable, contributions welcome.