ProjectExplorer: Introduce a ProjectConfiguration::kit() function

For convenience, and use it in some places.

Change-Id: I8f7cb502b37b2fbf4cf2d17cac9c6299558332dc
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/projectconfiguration.cpp

@@ -206,6 +206,11 @@ Project *ProjectConfiguration::project() const
     return m_target->project();
 }
 
+Kit *ProjectConfiguration::kit() const
+{
+    return m_target->kit();
+}
+
 Utils::Id ProjectConfiguration::id() const
 {
     return m_id;