conform to the spec: paths for File and Directory inputs placed in the InitialWorkDir must reflect that location and no other

Hi!

I think it would be useful/more clear if it is somehow possible to have access to the full path of a file that is marked `writable` in `InitialWorkDirRequirement`. Currently you just have to assume it will be in the current work folder (workdir) and you can access it with the basename flag of in the input.

Is it an idea to add a entry for path to the writable content?

It get specifically ambiguous if you use a `$(JSON.stringify(inputs))` in the `InitialWorkDirRequirement` listing, since once inside the container you can't know which item is flagged writable or not.