Handle Cargo.toml manifests that are symlinks

[tmfink]

The canonicalize() function resolves symlinks, which would cause targets whose "Cargo.toml" is a symlink to be filtered out. This would cause cargo-fmt to print an error "Failed to find targets".

Resolves #6184

[tmfink]

To keep the logic more tolerant, I added an extra comparison of file paths without a call to canonicalize() and left the original canonicalize() comparison, but is the canonicalize() ever actually needed?

Do some platforms/OS/filesystems require canonicalize()? Perhaps Windows paths with backslashes?