[display] unicode characters in file paths of responses

It looks like Haxe's display protocol (or maybe Haxe in general?) is unable to deal with unicode characters in file paths. Prior to vshaxe 2.10.0, no display modes were working at all in projects that had unicode characters somewhere in their path. Now, vshaxe uses relative file paths, which works around the issue.

However, this doesn't help for display modes that also _return_ paths as part of their responses (since those are always absolute). This affects diagnostics, statistics, goto definition / type definition...

To reproduce:

- move a project such as HaxeRepro into a folder with unicode characters such as `Алексей`
- open the project in VSCode
- add something that produces a diagnostics message such as an unused import
- observe that the unicode component of the path has been replaced by a single dot in the display response, e.g. `"C:\\Users\\Jens\\GitHub\\.\\HaxeRepro\\source\\Main.hx"`