Pull out some logic into generic functions for FileSystemProviders

[traeok]

Is your feature request related to a problem? Please describe.

While the logic is similar between Data Sets and USS for some of the filesystem functions, there are nuances that make it hard to avoid code duplication. That said, it would still be nice to pull some logic into common functions so it can be used across both filesystem implementations.

Describe the solution you'd like

Investigate readFile, writeFile and readDirectory functions for both filesystems and pull out common code into generic functions where possible.

Describe alternatives you've considered

We can keep the code as-is, but if we can consolidate more shared code, it will make it easier to maintain moving forward.