os: expand support for Windows Deduplication Reparse Points to Include SIS (NTFS)

[upgrade0217]

I ran into an issue using restic where Windows SIS reparse points on an NTFS file system were failing to back up. After some discussion, it was pointed out that the new Windows NTFS deduplication is supported nicely in Go.

Here is where I was shown support for the new Windows NTFS deduplication scheme: (https://tip.golang.org/src/os/types_windows.go#L201. I'm not 100% sure, but I think the old-style SIS deduplication could be handled the same way, just with a different reparse tag.

[cagedmantis]

@golang/windows

[gopherbot]

Change https://go.dev/cl/568535 mentions this issue: os: added support for SIS-deduplicated files on Windows

[mister-sir]

I submitted a change that should fix this. I unfortunately don't have easy access to a Windows box that I can build go on, so I wasn't able to fully test the change. It seems fairly straightforward, but it would be awesome if someone with Windows could test this.

[mister-sir]

Built and tested on Windows, just awaiting code review.

[qmuntal]

It looks like SIS dedup is deprecated since Windows Server 2012 R2 and removed in Windows Server 2016 in favor of Data Deduplication, as per Microsoft docs. Considering that the minimum supported version is Windows Server 2016, then I'm afraid that special-casing IO_REPARSE_TAG_SIS would be out of policy.

Even with that, IMO the Go standard library can't special-case all reparse points at will. Downstream apps should decide what to do with them in a case-by-case basis.