ProjectExplorer: Modernize even more

Use unique_ptr for all *Private classes, except for those
in singletons.

Change-Id: Ib56c31ddedc6e9cf321f15de1f1e697a27ad4089
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/projectexplorer/projectwindow.h

@@ -29,6 +29,8 @@
 
 #include <utils/fancymainwindow.h>
 
+#include <memory>
+
 namespace ProjectExplorer {
 namespace Internal {
 
@@ -59,7 +61,7 @@ public:
     ~ProjectWindow() override;
 
 private:
-    ProjectWindowPrivate *d;
+    const std::unique_ptr<ProjectWindowPrivate> d;
 };
 
 } // namespace Internal