Refactor startswith with path_isin util

[skshetry]

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Description

Resolves #2823

I did not feel brave enough on dvc.remote.s3.RemoteS3.exists.
EDIT: dvc.remote.s3.RemoteS3.exists cannot be changed, as path_isin is os-agnostic, whereas s3 requires posixpath. dvc/utils/__init__.py:260 has a cyclic dependency problem.

There are few other cases of startswith, but are not related with filepaths (except for dvc/utils/__init__.py at the end ⏬)

➜ rg -i startswith dvc tests
dvc/prompt.py
48:    return answer and answer.startswith("y")
dvc/remote/http.py
76:        if etag.startswith("W/"):
dvc/remote/config.py
97:        if remote == RemoteLOCAL and not url.startswith("remote://"):
tests/func/test_repro.py
1076:        assert i.startswith(prefix) and o.startswith(prefix)
1588:    elif line.startswith("cmd: "):
dvc/utils/fs.py
147:    return child != parent and child.startswith(parent)
dvc/utils/__init__.py
260:            while parts[0].startswith(plugin_bin):

Thank you for the contribution - we'll try to review it as soon as possible. 🙏

[ghost]

thanks a lot, @skshetry !

[ghost]

@skshetry , for S3 we use posixpath, if path_isin works for both POSIX and Windows, you can substitute it.

When working with CloudInfoURL you need to use .path to retrieve the path from the whole URL, for example: https://example.com/foo.path -> foo.

[skshetry]

@MrOutis, yes, path_isin supports both kind of paths. I'll push a change for s3 in a different commit, and you can give me feedback, if it's correct.

[efiop]

Nicely done, thank you!