Preserve trailing newline in TerminalOutput::full_text (#38061)

Closes #30678

This is caused by `TerminalOutput::full_text` triming trailing newline
when creating the "REPL Output" buffer.

Release Notes:

- fix: Preserve trailing newline in `TerminalOutput::full_text`

crates/repl/src/outputs/plain.rs

@@ -231,8 +231,7 @@ impl TerminalOutput {
             }
         }
 
-        // Trim any trailing newlines
-        full_text.trim_end().to_string()
+        full_text
     }
 }