fix: Use dunce crate to get non-UNC paths when calling canonicalize

[ericswanson-dfinity]

Description

Call dunce::canonicalize rather than Path::canonicalize. On Linux/Macos, this just calls std::fs::canonicalize(), so no change there.

PathBuf::canonicalize on Windows generally returns Windows NT UNC paths like \\?\C:\Users\you\. Lots of programs, including Microsoft's, don't work with these kinds of paths. For example, npm will print out a message something like The current working directory is a UNC path. I'm going to use C:\Windows instead..

dunce:

... converts paths to legacy format whenever possible, but leaves UNC paths as-is when they can’t be unambiguously expressed in a simpler way. This allows legacy programs to access all paths they can possibly access, and UNC-aware programs to access all paths.

rust-lang/rust#42869 (comment)

Part of https://dfinity.atlassian.net/browse/SDK-1343

How Has This Been Tested?

Covered by existing tests on Linux/Macos.

Checklist:

I didn't put anything in the changelog because we don't release for Windows and there is no behavior change on Linux/Macos.

• The title of this PR complies with Conventional Commits.