Fixed non-emit of NodeDelegateModel::in/outputConnectionCreated/Deleted.

The four virtual functions in NodeDelegateModel were not being called
anywhere in code as the logic was removed when FlowScene.cpp was removed
as part of the v3 upgrade.

This functionality has been restored thanks to two new functions
`DataFlowGraphModel::sendConnectionCreation` and
`DataFlowGraphModel::sendConnectionDeletion` which call the slots on
both the input and output nodes of any given connection.

Functions are:
- inputConnectionCreated
- inputConnectionDeleted
- outputConnectionCreated
- outputConnectionDeleted

Signed-off-by: Finn Rayment <finn@rayment.fr>

include/QtNodes/internal/DataFlowGraphModel.hpp

@@ -100,6 +100,10 @@ class NODE_EDITOR_PUBLIC DataFlowGraphModel : public AbstractGraphModel, public
 private:
     NodeId newNodeId() override { return _nextNodeId++; }
 
+    void sendConnectionCreation(ConnectionId const connectionId);
+
+    void sendConnectionDeletion(ConnectionId const connectionId);
+
 private Q_SLOTS:
     /**
    * Fuction is called in three cases:

include/QtNodes/internal/NodeDelegateModel.hpp

@@ -17,7 +17,7 @@ class StyleCollection;
 /**
  * The class wraps Node-specific data operations and propagates it to
  * the nesting DataFlowGraphModel which is a subclass of
- * AbstractGrapModel.
+ * AbstractGraphModel.
  * This class is the same what has been called NodeDataModel before v3.
  */
 class NODE_EDITOR_PUBLIC NodeDelegateModel : public QObject, public Serializable

src/DataFlowGraphModel.cpp

@@ -132,7 +132,7 @@ void DataFlowGraphModel::addConnection(ConnectionId const connectionId)
 {
     _connectivity.insert(connectionId);
 
-    Q_EMIT connectionCreated(connectionId);
+    sendConnectionCreation(connectionId);
 
     QVariant const portDataToPropagate = portData(connectionId.outNodeId,
                                                   PortType::Out,
@@ -146,6 +146,34 @@ void DataFlowGraphModel::addConnection(ConnectionId const connectionId)
                 PortRole::Data);
 }
 
+void DataFlowGraphModel::sendConnectionCreation(ConnectionId const connectionId)
+{
+    Q_EMIT connectionCreated(connectionId);
+
+    auto iti = _models.find(connectionId.inNodeId);
+    auto ito = _models.find(connectionId.outNodeId);
+    if (iti != _models.end() && ito != _models.end()) {
+        auto &modeli = iti->second;
+        auto &modelo = ito->second;
+        modeli->inputConnectionCreated(connectionId);
+        modelo->outputConnectionCreated(connectionId);
+    }
+}
+
+void DataFlowGraphModel::sendConnectionDeletion(ConnectionId const connectionId)
+{
+    Q_EMIT connectionDeleted(connectionId);
+
+    auto iti = _models.find(connectionId.inNodeId);
+    auto ito = _models.find(connectionId.outNodeId);
+    if (iti != _models.end() && ito != _models.end()) {
+        auto &modeli = iti->second;
+        auto &modelo = ito->second;
+        modeli->inputConnectionDeleted(connectionId);
+        modelo->outputConnectionDeleted(connectionId);
+    }
+}
+
 bool DataFlowGraphModel::nodeExists(NodeId const nodeId) const
 {
     return (_models.find(nodeId) != _models.end());
@@ -355,7 +383,7 @@ bool DataFlowGraphModel::deleteConnection(ConnectionId const connectionId)
     }
 
     if (disconnected) {
-        Q_EMIT connectionDeleted(connectionId);
+        sendConnectionDeletion(connectionId);
 
         propagateEmptyDataTo(getNodeId(PortType::In, connectionId),
                              getPortIndex(PortType::In, connectionId));