Convert more ShellError variants to named fields (#11222)

# Description

Convert errors to named fields:
* NeedsPositiveValue
* MissingConfigValue
* UnsupportedConfigValue
* DowncastNotPossible
* NonUtf8Custom
* NonUtf8
* DidYouMeanCustom
* DidYouMean
* ReadingFile
* RemoveNotPossible
* ChangedModifiedTimeNotPossible
* ChangedAccessTimeNotPossible

Part of #10700

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

@@ -52,11 +52,11 @@ impl Command for HideEnv {
                     .cloned()
                     .collect();
                 if let Some(closest_match) = did_you_mean(&all_names, &name.item) {
-                    return Err(ShellError::DidYouMeanCustom(
-                        format!("Environment variable '{}' not found", name.item),
-                        closest_match,
-                        name.span,
-                    ));
+                    return Err(ShellError::DidYouMeanCustom {
+                        msg: format!("Environment variable '{}' not found", name.item),
+                        suggestion: closest_match,
+                        span: name.span,
+                    });
                 } else {
                     return Err(ShellError::EnvVarNotFoundAtRuntime {
                         envvar_name: name.item,

crates/nu-cmd-lang/src/core_commands/overlay/use_.rs

@@ -96,7 +96,9 @@ impl Command for OverlayUse {
             if let Some(name) = os_str.to_str() {
                 name.to_string()
             } else {
-                return Err(ShellError::NonUtf8(name_arg.span));
+                return Err(ShellError::NonUtf8 {
+                    span: name_arg.span,
+                });
             }
         } else {
             return Err(ShellError::OverlayNotFoundAtRuntime {