hard-code selection color to be reverse (#14052)

# Description

This PR makes visual selection in Nushell a little bit more readable.

### Before

![image](https://github.com/user-attachments/assets/3020abd2-c02c-4f16-b68a-cbe72278cbc8)

### After

![image](https://github.com/user-attachments/assets/fcf919fa-bc02-449b-b5bc-ed05959cc7de)

# User-Facing Changes
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crates/nu-cli/src/repl.rs

@@ -376,7 +376,11 @@ fn loop_iteration(ctx: LoopContext) -> (bool, Stack, Reedline) {
                 .to_string_lossy()
                 .to_string(),
         ))
-        .with_cursor_config(cursor_config);
+        .with_cursor_config(cursor_config)
+        .with_visual_selection_style(nu_ansi_term::Style {
+            is_reverse: true,
+            ..Default::default()
+        });
 
     perf!("reedline builder", start_time, use_color);