gh-69134: Wait until mapped in SimpleDialog keyboard tests

The SimpleDialog tests generate key events after focus_force().  On
Windows these are only delivered once the toplevel is mapped, so they
could be dropped and the test fail intermittently (seen on the Windows10
buildbot as test_return_no_default).  Unlike the query dialogs,
SimpleDialog only waits for its window in go(), which these tests bypass,
so wait until it is mapped in the create() helper, 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 +23,11 @@ def create(self, **kw):
         kw.setdefault('cancel', 1)
         d = SimpleDialog(self.root, **kw)
         self.addCleanup(lambda: d.root.winfo_exists() and d.root.destroy())
+        # Unlike the query dialogs, SimpleDialog only waits for the window to
+        # appear in go(), which these tests bypass.  On Windows the generated
+        # key events are dropped until the toplevel is mapped (gh-69134), so
+        # wait for it here.
+        self.require_mapped(d.root)
         return d
 
     # --- Widget set and appearance ---