Fix getting position of wxPopupWindow in wxMSW.

Don't offset the returned values by the parent window origin unnecessarily: as
popup windows are created as children of the desktop window in wxMSW, their
coordinates are already expressed in screen coordinate system (which is
exactly the same as display window coordinate system) and we must not try to
translate them to it once again, this is completely wrong and was probably a
left over from earlier wxPopupWindow implementation in which it wasn't created
as a child of desktop.

Closes #4440.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76675 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix changing the label of a submenu in wxMSW.

Use position, not the ID, to find the native menu items to allow the code in
wxMenuItem::SetItemLabel() and DoSetBitmap() to also work with submenus and
not just the normal items.

Closes #16246.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76676 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775