QmlDesigner: Add QML front-end for ConnectionView

This is still disabled by default until the UI gets polished.

Add roles to models. ConnectionModel, BindingModel and DynamicPropertiesModel.
In QML roles are used in the ListView to "mimic" columns. The columns are only
relevant for the "old" cpp QTableView and can be removed.

Making currentIndex part of the model. If rows are removed and added
again we have to "reset/keep" the currentIndex as part of the model, because
the index is temporarly invalid on the view.

Implementing DynamicPropertiesModelBackendDelegate as reference.
This is a pure "backend delegate" that exposes all relevant properties for
a current row to QML.

Adding StudioQuickWidget and exposing the backend.

Adding StudioQmlTextBackend and StudioQmlComboBoxBackend to
StudioQuickWidget (should be moved into their own files).
Those helper classes make is easy to expose a property to a combobox or
textfield. The backend has to know nothing about the actual frontend
and those classes act as a mini-model for a view in QML.
The API is similar to UI controls.

Change-Id: I7a2c6ad951306fbca1d586fb8f278acdd91a064b
Reviewed-by: Qt CI Patch Build Bot <ci_patchbuild_bot@qt.io>
Reviewed-by: Knud Dollereder <knud.dollereder@qt.io>

src/plugins/qmldesigner/components/connectioneditor/connectionmodel.cpp

@@ -252,6 +252,19 @@ void ConnectionModel::updateCustomData(QStandardItem *item, const SignalHandlerP
 {
     item->setData(signalHandlerProperty.parentModelNode().internalId(), UserRoles::InternalIdRole);
     item->setData(signalHandlerProperty.name(), UserRoles::TargetPropertyNameRole);
+    item->setData(signalHandlerProperty.parentModelNode()
+                      .bindingProperty("target")
+                      .resolveToModelNode()
+                      .id(),
+                  UserRoles::TargetNameRole);
+
+    // TODO signalHandlerProperty.source() contains a statement that defines the type.
+    // foo.bar() <- function call
+    // foo.state = "literal" //state change
+    //anything else is assignment
+    // e.g. foo.bal = foo2.bula ; foo.bal = "literal" ; goo.gal = true
+
+    item->setData("Assignment", UserRoles::ActionTypeRole);
 }
 
 ModelNode ConnectionModel::getTargetNodeForConnection(const ModelNode &connection) const
@@ -370,6 +383,16 @@ void ConnectionModel::removeRowFromTable(const SignalHandlerProperty &property)
     }
 }
 
+void ConnectionModel::add()
+{
+    addConnection();
+}
+
+void ConnectionModel::remove(int row)
+{
+    deleteConnectionByRow(row);
+}
+
 void ConnectionModel::handleException()
 {
     QMessageBox::warning(nullptr, tr("Error"), m_exceptionError);
@@ -522,4 +545,12 @@ QStringList ConnectionModel::getPossibleSignalsForConnection(const ModelNode &co
     return stringList;
 }
 
+QHash<int, QByteArray> ConnectionModel::roleNames() const
+{
+    static QHash<int, QByteArray> roleNames{{TargetPropertyNameRole, "signal"},
+                                            {TargetNameRole, "target"},
+                                            {ActionTypeRole, "action"}};
+    return roleNames;
+}
+
 } // namespace QmlDesigner