Differential Slices for Servicing Updates

This would probably be very tricky to implement, but we could improve upon the differential when building servicing releases by only copying the files that had changed.

This would require us to:
- fetch the "base" release (e.g. 7.4.0)
- Get the latest service release (e.g. 7.4.2)
- Find only the files that have changed since the last release. The .NET BCL DLLs should all stay the same so it should mostly just be SMA and a handful of others
- Copy those files into a new layer

Now when you update from 7.4.2 to 7.4.1, you're downloading a layer that basically only has the changed SMA files rather than what is basically a full zip of the PowerShell installation.

There's little point in doing this between .NET versions since 90% of it will have changed, but it might be a good approach for servicing releases.

This is probably more minmaxxing then is worth the effort, but I might try it just to take on a challenge.