Refactored class, include and package diagrams visitor to output filtered intermediate diagram (#289)

src/common/model/diagram_element.h

@@ -26,11 +26,14 @@
 
 #include <atomic>
 #include <exception>
+#include <set>
 #include <string>
 #include <vector>
 
 namespace clanguml::common::model {
 
+class diagram_filter;
+
 /**
  * @brief Base class for standalone diagram elements.
  *
@@ -184,6 +187,9 @@ public:
      */
     void complete(bool completed);
 
+    virtual void apply_filter(
+        const diagram_filter &filter, const std::set<eid_t> &removed);
+
 private:
     eid_t id_{};
     std::optional<eid_t> parent_element_id_{};