Improve error message for illegal filenames on Windows (#7348)

`ls` can fail when a directory contains a file that violates [the
Windows file naming
conventions](https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions).
This PR tweaks the error message so we tell the user _which_ file caused
the problem.

Closes #7345.

### Before:

![image](https://user-images.githubusercontent.com/26268125/205508355-2875f851-6b61-4897-97b8-9094b24ea197.png)

### After:


![image](https://user-images.githubusercontent.com/26268125/205508325-0b4efd25-b454-4d1b-b8e9-cb26803fbcff.png)


## Future Work

Like Chris said in the linked issue, it would be even better if Nu could
just handle these naughty files like cmd.exe and pwsh do. If someone has
the time to dive into how PowerShell does this, that would be much
appreciated.

crates/nu-command/src/filesystem/ls.rs

@@ -799,7 +799,10 @@ mod windows_helper {
             .is_err()
             {
                 return Err(ShellError::ReadingFile(
-                    "Could not read file metadata".to_string(),
+                    format!(
+                        "Could not read metadata for '{}'. It may have an illegal filename.",
+                        filename.to_string_lossy()
+                    ),
                     span,
                 ));
             }