QmakeProjectManager: Make target search operate on project nodes

This makes the using code a bit less dependent on qmake specifics
(qmake related ProjectNode specialization vs qmake-only class)

Change-Id: Ied6ced70694b3ac0665d88ec86c4a66577f3a672
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qmakeprojectmanager/qmakenodes.cpp

@@ -307,4 +307,9 @@ QString QmakeProFileNode::objectExtension() const
     return exts.first();
 }
 
+TargetInformation QmakeProFileNode::targetInformation() const
+{
+    return proFile() ? proFile()->targetInformation() : TargetInformation();
+}
+
 } // namespace QmakeProjectManager