Add file details

[richardschneider]

As a developer
I want to know all blocks and serialisaton size when a file/directory is added
So that I can use a Storage Market to replicate the file

Currently, the file system Add methods only return the top FileSystemNode, then I need to call ObjectApi.LinksAsync to get the sub-blocks and then recurse on the links for other links. This is all very inefficient.

Need to have new Add methods that return a sequence of FileSystemNode, where the last element is the "top" node.