Fix memory leak in connection graph

When generating virtual connections to represent bus aliases, we need to
store the pointers for future deletion otherwise we will leak the memory

(cherry picked from commit 9260f58803)

eeschema/connection_graph.cpp

@@ -1367,11 +1367,15 @@ void CONNECTION_GRAPH::generateBusAliasMembers()
                 wxString name = conn->FullLocalName();
 
                 CONNECTION_SUBGRAPH* new_sg = new CONNECTION_SUBGRAPH( this );
+
+                // This connection cannot form a part of the item because the item is not, itself
+                // connected to this subgraph.  It exists as part of a virtual item that may be connected
+                // to other items but is not in the schematic.
                 SCH_CONNECTION* new_conn = new SCH_CONNECTION( item, subgraph->m_sheet );
                 new_conn->SetGraph( this );
-
                 new_conn->SetName( name );
                 new_conn->SetType( CONNECTION_TYPE::NET );
+                subgraph->StoreImplicitConnection( new_conn );
                 int code = assignNewNetCode( *new_conn );
 
                 wxLogTrace( ConnTrace, wxS( "SG(%ld), Adding full local name (%s) with sg (%d) "

eeschema/connection_graph.h

@@ -89,7 +89,11 @@ public:
               m_driver_connection( nullptr )
     {}
 
-    ~CONNECTION_SUBGRAPH() = default;
+    ~CONNECTION_SUBGRAPH()
+    {
+        for( SCH_CONNECTION* connection : m_bus_element_connections )
+            delete connection;
+    }
 
     friend class CONNECTION_GRAPH;
 
@@ -195,6 +199,13 @@ public:
 
     void RemoveItem( SCH_ITEM* aItem );
 
+    // Use this to keep a connection pointer that is not owned by any item
+    // This will be destroyed with the subgraph
+    void StoreImplicitConnection( SCH_CONNECTION* aConnection )
+    {
+        m_bus_element_connections.insert( aConnection );
+    }
+
 private:
     wxString driverName( SCH_ITEM* aItem ) const;
 
@@ -286,6 +297,10 @@ private:
 
     /// Cache for driver connection.
     SCH_CONNECTION* m_driver_connection;
+
+    /// A cache of connections that are part of this subgraph but that don't have
+    /// an owning element (i.e. bus members)
+    std::set<SCH_CONNECTION*> m_bus_element_connections;
 };
 
 struct NET_NAME_CODE_CACHE_KEY