Implement IFileSystem.MoveFile on AzureBlobFileSystem #81
Description
With this PR I had a need for a MoveFile method, that I was surprised to find isn't available on IFileSystem. It will be added when the PR is merged and released for 17.1.
I've added a default implementation for the method such that it'll work for any concrete implementations of IFileSystem that haven't explicitly implemented it, but it would likely be more performant if they did.
Hence raising this issue so it can be considered for adding support for in this library, once 17.1 is out.