Add ErrSpan extension trait for Result (#12626)

# Description
This adds an extension trait to `Result` that wraps errors in `Spanned`,
saving the effort of calling `.map_err(|err| err.into_spanned(span))`
every time. This will hopefully make it even more likely that someone
will want to use a spanned `io::Error` and make it easier to remove the
impl for `From<io::Error> for ShellError` because that doesn't have span
information.

crates/nu-cmd-lang/src/core_commands/do_.rs

@@ -117,7 +117,7 @@ impl Command for Do {
                                     None,
                                 )
                             })
-                            .map_err(|e| e.into_spanned(call.head))
+                            .err_span(call.head)
                     })
                     .transpose()?;