QmlDesigner: Do not require a qmake project for designer import paths

Let's enable all build system plugins to provide this information.

Task-number: QTCREATORBUG-20810
Change-Id: I0ef953e3c2c9a2be1fc4187e93232e9a2aeacafd
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/projectexplorer/project.cpp

@@ -855,6 +855,13 @@ Utils::MacroExpander *Project::macroExpander() const
     return &d->m_macroExpander;
 }
 
+QVariant Project::additionalData(Core::Id id, const Target *target) const
+{
+    Q_UNUSED(id);
+    Q_UNUSED(target);
+    return QVariant();
+}
+
 bool Project::isParsing() const
 {
     return d->m_isParsing;