TextEditor: add text cursor to assist interface

This will allow us to request assistance for a specific selection
instead of just the position.

Change-Id: Ib8e5b32d4a8f2936e5a6f1b7ac968d7f1d8d9de6
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qmldesigner/components/bindingeditor/bindingeditorwidget.cpp

@@ -103,7 +103,7 @@ TextEditor::AssistInterface *BindingEditorWidget::createAssistInterface(
 {
     Q_UNUSED(assistKind)
     return new QmlJSEditor::QmlJSCompletionAssistInterface(
-                document(), position(), Utils::FilePath(),
+                textCursor(), Utils::FilePath(),
                 assistReason, qmljsdocument->semanticInfo());
 }