Partially revert the changes of r69350 to restore EVT_IDLE handling of wxPopupTransientWindow under MSW. It turns out that we must release the mouse for the embedded controls to work. It would be better to solve the problem differently, e.g. perhaps maybe only releasing mouse capture when mouse is clicked as the current code is fragile but for now at least restore the functionality that used to work. Closes #13740. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69966 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775