Add OsString support to windows-registry crate

[kennykerr]

Fixes: #3119

[kennykerr]

Wow, that's quite the bizarre nightly behavior. 🤪

[kennykerr]

Looks like that's a rustfmt bug:

rust-lang/rustfmt#6210
rust-lang/rust#126888

[ChrisDenton]

Looks good to me. Seems like the rustfmt bug will fix itself in the next nightly.

[ChrisDenton]

Oh it just occurred to me that maybe we could just return a HSTRING or a Vec<u16> and let users turn that into a OsString or whatever they want. It's less ergonomic for the OsString case but more flexible in general.

[kennykerr]

Yes, I thought about using HSTRING instead. It's way better and provides convertibility with OsString. I just need to pull HSTRING and friends into a new windows-strings crate before I can add a dependency from windows-registry. I need to do that anyway, so perhaps I'll wait on this PR and we can just use HSTRING here.

[ChrisDenton]

To be honest, that does sound a lot more appealing to me now that I've considered it some more.