[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 think the `"translog-"` string should be a public global static var named `TRANSLOG_FILENAME_PREFIX`, and should be used as the glob pattern for the directory stream. Then all the hardcoded "translog-" strings in here can use the PREFIX var (I did this the hard way in my version of the branch where I typo'd the prefix and it took forever to debug, so having a static prefix to use would be nice).

This PREFIX can also be used in `LocalIndexShardGateway.recover` since it's hardcoded to `"translog-" + id` there too.