[TRANSLOG] Cut over to Path API

This commit also refactors `RAFReference` to work on top of a Channel instead of fetching the channel from the RandomAccessFile. The channel is created to truncate the file it opens too. This likely needs some documentation or we should allow the caller to pass the open options but I wanted to get this change out for review.
I only mentioned it because if we really have to keep this, then StandardOpenOption.DELETE_ON_CLOSE could be an implementation. But this one has race conditions too, this delete-on-close stuff is why Lucene's lockfactories were buggy for years. Lets defer it to a new issue, ideally we just nuke it completely.