gh-69134: Wait until mapped in SimpleDialog keyboard tests

The SimpleDialog tests generate key events after focus_force(), which on
Windows are dropped until the toplevel is mapped.  Wait until it is
mapped, as GH-152599 did for the other keyboard tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_tkinter/test_simpledialog.py

@@ -23,6 +23,9 @@ def create(self, **kw):
         kw.setdefault('cancel', 1)
         d = SimpleDialog(self.root, **kw)
         self.addCleanup(lambda: d.root.winfo_exists() and d.root.destroy())
+        # On Windows the generated key events are dropped until the
+        # toplevel is mapped (gh-69134).
+        self.require_mapped(d.root)
         return d
 
     # --- Widget set and appearance ---