Generate unshifted Unicode key codes in wxEVT_KEY_XXX events in wxGTK.

Generate unshifted Unicode key codes in wxEVT_KEY_XXX events in wxGTK.

wxGTK generated wxEVT_KEY_XXX with key codes corresponding to the unshifted
state of the key (except for the letters) but Unicode key codes corresponding
to the current shift state. This was inconsistent with wxMSW and also with the
idea that key events, unlike char ones, don't depend on the modifiers states.

Change wxGTK to behave as wxMSW and use unshifted values for Unicode key codes
as well.

Remove the now unnecessary workaround for different key event Unicode codes
from test.

Also try to explain the difference between normal and Unicode keys and key and
char events even better and mention that the Unicode key codes for the key
events are also untranslated in the documentation.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65526 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775