Use prompt_toolkit's patch_stdout_context when finding completions

Closes gh-10113

IPython/terminal/ptutils.py

@@ -37,6 +37,10 b' class IPythonPTCompleter(Completer):'
         if not document.current_line.strip():
             return
 
+        # Some bits of our completion system may print stuff (e.g. if a module
+        # is imported). This context manager ensures that doesn't interfere with
+        # the prompt.
+        with self.shell.pt_cli.patch_stdout_context():
         used, matches = self.ipy_completer.complete(
                             line_buffer=document.current_line,
                             cursor_pos=document.cursor_position_col