Align path format for windows.

[specter119]

This PR makes the following modifications.

overall:

• change str(pathlib.Path) to pathlib.Path.as_posix()
• convert pathlib.Path / "a" / "b" / "c" to pathlib.Path / "a/b/c"
• replace parent.parent with parents[1]

for plugins/lab/fps_lab/utils.py:

• use pathlib.Path.rglob to replace glob.glob(pathlib.Path, recursive=True)
• check "jupyterlab" in package

---

With these modifications, the following issues on the windows platform solved:

• no labextension is found.
• in the file browser, the path is not separated (displayed as / a\b\c /, and can't enter the parent folder).
• raise error the package.json without "jupyterlab"

however, the following errors still exist, and I'm not sure they're windows specific:

• --root-path doesn't change the root folder, and the root folder is still .
• the pwd is always the root folder and doesn't change following the editing file.

---

To sum up, the unix like path is more friendly even in the windows platform, but str(pahtlib.Path) will convert the path as the native format.

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[davidbrochart]

Thanks a lot @specter119!
I'm wondering if we should use as_posix() only when passing paths to the front-end, and not use it or forward slashes (/) in the back-end.

[davidbrochart]

Is the hard-coded / going to play well on Windows?

[specter119]

yes, hard-code /, works as excepted.

[davidbrochart]

From what I can read, I think it works because Python does some tricks to convert forward slashes to backslashes if needed when opening files, but the best practice is still to use pathlib's / operator.

[specter119]

revert these changes.

[davidbrochart]

• --root-path doesn't change the root folder, and the root folder is still .
• the pwd is always the root folder and doesn't change following the editing file.

We currently don't handle a root directory (see #236), but we definitely need this.

[specter119]

I add these changes to my local jupyverse, and it works as excepted. Together, I will actively use jupyverse for a perioid of time. Since the behavior of jupyter-server (maybe related with tornado) break my daily work, and downgrade to tornado 6.1 doesn't help.

[davidbrochart]

Yes, jupyter-server's dependency on Tornado was one of the reasons to start jupyverse.

[davidbrochart]

Thanks Kyle, just a minor change.

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