feat: use std::path::Path for fs backend

[baszalmstra]

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Summary

As discussed in #137 this PR changes the internals of the fs backend to use std::path::Path. This enables using all the path types that std::path::Path supports like Windows disk drive prefixes and network drives.

This is my first contribution! Im looking forward to your feedback!

[baszalmstra]

The unit_oli test also seems to fail. Additionally, when no root is specified the fs backend was previously by default rooted at /. However, that doesn't exist on windows. What would be a good alternative?

[Xuanwo]

when no root is specified the fs backend was previously by default rooted at /.

On windows, fs backend must specify a root-like C:/. We can implement different test for windows.

[Xuanwo]

Hi, in PR #1221, I make opendal's test buildable on windows.

[wolfv]

Nice @Xuanwo !

[baszalmstra]

Awesome thanks! I will integrate!

[baszalmstra]

I redid the whole thing from scratch. I got all opendal's tests working (at least locally).

The only thing I don't know how to solve exactly is using an empty root for the Fs backend. I currently implemented that this will use the current directory because that's consistent on all platforms. Previously this would default to / but on windows, no such directory actually exists and there is also no sensible default. Would it be C:\? Should it be the drive of the current directory? You also can't use an "empty" root because C:\bla.txt is not a valid path for opendal.

Curious about what you think!

[Xuanwo]

I currently implemented that this will use the current directory because that's consistent on all platforms.

LGTM!

[Xuanwo]

This PR looks nice now, please update with main branch and make our CI passed on windows platform (fs local test)

[Xuanwo]

Thanks a lot!