Avoid unnecessary copies of Thrift binary types

[ctubbsii]

No description provided.

[DomGarguilo]

In #6430, I suggested ByteBufferUtil because it preserved the original behavior: the old code read from ByteBuffer fields and made defensive copies. Without that, the new object may reuse Thrift’s internal byte array, so changes to the Thrift object could also change the constructed Key/Column/Mutation.

That being said, if it doesn't seem like that is an issue here, I think this is a good fix for the mentioned issue we are seeing.

[ctubbsii]

Closing due to discussion on #6455 ; I didn't realize the getter was also calling the setter.