Correct window transparency calculation in wxQT, thanks @seandpagnier

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77931 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Copy pixmap to match others ctors in wxQT, thanks @seandpagnier

This should fix a double free crash

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77932 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Implement readonly dcscreen for wxQT, thanks @seandpagnier

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77933 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Remove redundant __WXQT__ define, thanks @seandpagnier

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77934 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775