[3.15] gh-69134: Wait until mapped in keyboard virtual-event tests (GH-152599) (GH...

[3.15] gh-69134: Wait until mapped in keyboard virtual-event tests (GH-152599) (GH-152605)

test_virtual_events and test_selection_event 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.  Wait until the
widget is mapped, as the other GUI tests already do.
(cherry picked from commit be4eebb8386d07f360dd835a0ecb4a1eb6385736)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>