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-command/src/filesystem/save.rs

@@ -133,7 +133,7 @@ impl Command for Save {
                                     .spawn(move || stderr.drain()),
                             })
                             .transpose()
-                            .map_err(|e| e.into_spanned(span))?;
+                            .err_span(span)?;
 
                         let res = stream_to_file(stdout, file, span, progress);
                         if let Some(h) = handler {

crates/nu-command/src/filters/tee.rs

@@ -125,8 +125,7 @@ use it in your pipeline."#
                 if use_stderr {
                     let stderr = stderr
                         .map(|stderr| {
-                            let iter = tee(stderr.stream, with_stream)
-                                .map_err(|e| e.into_spanned(call.head))?;
+                            let iter = tee(stderr.stream, with_stream).err_span(call.head)?;
                             Ok::<_, ShellError>(RawStream::new(
                                 Box::new(iter.map(flatten_result)),
                                 stderr.ctrlc,
@@ -146,8 +145,7 @@ use it in your pipeline."#
                 } else {
                     let stdout = stdout
                         .map(|stdout| {
-                            let iter = tee(stdout.stream, with_stream)
-                                .map_err(|e| e.into_spanned(call.head))?;
+                            let iter = tee(stdout.stream, with_stream).err_span(call.head)?;
                             Ok::<_, ShellError>(RawStream::new(
                                 Box::new(iter.map(flatten_result)),
                                 stdout.ctrlc,
@@ -189,7 +187,7 @@ use it in your pipeline."#
                     // Make sure to drain any iterator produced to avoid unexpected behavior
                     result.and_then(|data| data.drain())
                 })
-                .map_err(|e| e.into_spanned(call.head))?
+                .err_span(call.head)?
                 .map(move |result| result.unwrap_or_else(|err| Value::error(err, closure_span)))
                 .into_pipeline_data_with_metadata(metadata, engine_state.ctrlc.clone());
 

crates/nu-command/src/system/complete.rs

@@ -62,7 +62,7 @@ impl Command for Complete {
                                 }
                             })
                             .map(|handle| (handle, stderr_span))
-                            .map_err(|err| err.into_spanned(call.head))
+                            .err_span(call.head)
                     })
                     .transpose()?;
 

crates/nu-command/src/system/run_external.rs

@@ -495,7 +495,7 @@ impl ExternalCommand {
 
                                 Ok(())
                             })
-                            .map_err(|e| e.into_spanned(head))?;
+                            .err_span(head)?;
                     }
                 }
 
@@ -580,7 +580,7 @@ impl ExternalCommand {
                             Ok(())
                         }
                     })
-                    .map_err(|e| e.into_spanned(head))?;
+                    .err_span(head)?;
 
                 let exit_code_receiver = ValueReceiver::new(exit_code_rx);