Fix handling of Esc while an auto-complete drop down is open in wxMSW.

Just close the drop down instead of closing the dialog the text control using
this auto-complete drop down is in, as this was completely unexpected and
counter-intuitive.

Closes #13945.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76097 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775