QmlDesigner: add verification that the function exists

Add verification that the function exists before invoking it.
It causes warnings when the method does not exist in a pane.
Also all of the panes don't need this.

In addition, removing the placeholder with an empty function,
as it is no longer needed.

Task-number: QDS-14709
Change-Id: Ieaff5cf4759514c84e09ca0faaecc22b357b9a94
Reviewed-by: Ali Kianian <ali.kianian@qt.io>
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/emptyPane.qml

@@ -13,11 +13,6 @@ Rectangle {
     height: 400
     color: StudioTheme.Values.themePanelBackground
 
-    // Called from C++ to clear the search when the selected node changes
-    function clearSearch() {
-        // The function is empty, because it is a placeholder to match other panes
-    }
-
     ColumnLayout {
         id: mainColumn
         anchors.fill: parent

src/plugins/qmldesigner/components/propertyeditor/propertyeditorview.cpp

@@ -453,7 +453,14 @@ void PropertyEditorView::resetView()
 
     if (m_qmlBackEndForCurrentType) {
         m_qmlBackEndForCurrentType->emitSelectionChanged();
-        QMetaObject::invokeMethod(m_qmlBackEndForCurrentType->widget()->rootObject(), "clearSearch");
+
+        const auto qmlBackEndObject = m_qmlBackEndForCurrentType->widget()->rootObject();
+        if (qmlBackEndObject) {
+            const auto metaObject = qmlBackEndObject->metaObject();
+            const int methodIndex = metaObject->indexOfMethod("clearSearch()");
+            if (methodIndex != -1)
+                metaObject->method(methodIndex).invoke(qmlBackEndObject);
+        }
     }
 
     m_locked = false;