Add GdkEventKey declaration fix PCH-less build.

Declare it in wx/gtk/textentry.h too, not only wx/gtk/window.h.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73707 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775