fix: set the initial repl cursor pos, fixes #8943 (#8955)

# Description
Set the initial repl cursor pos, so running `commandline --insert`
inserts at the current cursor position of the input buffer.



Co-authored-by: sholderbach <sholderbach@users.noreply.github.com>

crates/nu-cli/src/repl.rs

@@ -477,6 +477,12 @@ pub fn evaluate_repl(
                     }
                 }
 
+                let mut repl_cursor = engine_state
+                    .repl_cursor_pos
+                    .lock()
+                    .expect("repl cursor pos mutex");
+                *repl_cursor = line_editor.current_insertion_point();
+                drop(repl_cursor);
                 let mut repl_buffer = engine_state
                     .repl_buffer_state
                     .lock()