macOS/Catalina: Modal File Dialog Save-Replace Always Rejected

When you create a modal native file dialog to save a file, and you wish to replace an existing file with the same name, macOS will prompt you if you wish to "Replace".  When you accept it, QFileDialog::exec() returns 0 (Rejected).  When not modal, 1 (Accepted) is returned.  We want to use modal and for it to appear as a sheet.  Bug #2: Whether you accept or cancel, selectedFiles() is always valid, so there is no secondary way of determining if the choice was truly rejected.

Example program attached.

This is Catalina specific. Works on Osx 10.14