Wrap Volume Mount Point management functions nicely for Go

[TBBle]

I'm talking specifically about:

• SetVolumeMountPoint
• DeleteVolumeMountPoint
• GetVolumeNameForVolumeMountPoint
• GetVolumePathNamesForVolumeName

Although these are exposed in raw-form (using *uint16) by "golang.org/x/sys/windows", it'd be handy to have Go-typed wrappers around them. Over the last fortnight, I've created two PRs in different projects using the same wrappers for the first two APIs (microsoft/hcsshim#852 and containerd/containerd#4419).

I'm happy to contribute a PR, but I'd like to confirm that this is the right repo to put those wrappers into? It seems to fit nicely with the exposed EncodeReparsePoint and DecodeReparsePoint which also live here.

[TBBle]

I just came across https://github.com/gentlemanautomaton/volmgmt which contains GetVolumeNameForVolumeMountPoint and GetVolumePathNamesForVolumeName but does not contain SetVolumeMountPoint or DeleteVolumeMountPoint.

That said, I already have (simple) implementations for the former two, I came across this repo while looking for APIs to use for formatting VHDs for a test.