Support getting a canonical file Path

[jeffdgr8]

Getting a file's canonical path is one of the few file APIs my library tests require that kotlinx-io doesn't currently support.

Similar API references:

• JVM File.getCanonicalPath
• Apple Foundation NSURL.canonicalPath
  
• Okio FileSystem.canonicalize

[jeffdgr8]

@fzhinkin I just checked out this new FileSystem.resolve(Path) API in 0.3.1. The issue I ran into is the fact that it throws FileNotFoundException when the file doesn't exist. Would it be possible to have a way to get a canonical path even for non-existent files?

[fzhinkin]

Yes, need to support canonicalization without link resolution.

[mipastgt]

I have to say that this missing feature makes the whole library currently unusable for me. I hope that this can be fixed soon.