Do use IsEscapeKey() in wxDialog escape key handling.

Do use IsEscapeKey() in wxDialog escape key handling.

This method was added back in r40686 but was never actually used anywhere. Do
use it in wxDialogBase::OnCharHook() now instead of hard-coding the check for
WXK_ESCAPE, this should allow using Cmd+. to work like Escape under Mac which
was apparently the intention of the code in src/osx/dialog_osx.cpp.

Also fix IsEscapeKey() itself to ignore any modifiers as at least under MSW
Esc always closes the dialog, even if Shift or Alt is pressed.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72610 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775