add a Storage Provider that works against an iOS or macOS provided fileURL

[heckj]

Add a built-in storage provider that is initialized with a fileURL, to accomodate the following use cases:

• a fileURL provided by NSDocument, UIDocument, or SwiftUI document-based APIs that points to a location on disk (for example, .fileImporter that returns a fileURL that then needs to be accessed as a security scoped URL - .startAccessingSecurityScopedResource())
• (This might be same as above, but a URL bookmark that was shared - https://developer.apple.com/documentation/security/app_sandbox/accessing_files_from_the_macos_app_sandbox)
• a constant or indicator that the storage provider should use the App's sandboxed Documents location
• an App Group container URL

[jessegrosjean]

I'm not sure if this would be right for the default file storage provider, but I've been playing with making NSDocument write to a bundle format using the general design suggested here for CloudKit .

The nice feature of this is that the format should then automatically merge. So for example you can share this on iCloud Drive and concurrent edits should converge.

Except my version seems to have bugs that I'm still figuring out :) Anyway, don't have anything fully working to share yet, just wanted to add this note for possible future implementation.

[heckj]

If you want to lift the logic, there's an implementation of the "partial incremental changes"/"compacted changes" in parallel in the DocumentStorage class of the repo - Following the JS impl, it was meant to ride about the provider, which is only concerned with shifting bytes onto, and off of, disk given various prefixes (used to determine locations)