fspath: allow unicode numbers and letters in remote names

Previously it was limited to plain ASCII (0-9, A-Z, a-z).

Implemented by adding \p{L}\p{N} alongside the \w in the regex,
even though these overlap it means we can be sure it is 100%
backwards compatible.

Fixes #6618

backend/drive/drive.go

@@ -3431,7 +3431,7 @@ func (f *Fs) Command(ctx context.Context, name string, arg []string, opt map[str
 		if err != nil {
 			return nil, err
 		}
-		re := regexp.MustCompile(`[^\w_. -]+`)
+		re := regexp.MustCompile(`[^\w\p{L}\p{N}. -]+`)
 		if _, ok := opt["config"]; ok {
 			lines := []string{}
 			upstreams := []string{}