QmlDesigner: Allow plain expressions to be set with LineEdit control

Task-number: QDS-2603
Change-Id: I10a1b513bc21b8736683d4ddc2e290c29b39696d
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/HelperWidgets/LineEdit.qml

@@ -40,6 +40,7 @@ StudioControls.TextField {
     translationIndicatorVisible: showTranslateCheckBox
 
     property bool writeValueManually: false
+    property bool writeAsExpression: false
 
     property bool __dirty: false
 
@@ -93,6 +94,9 @@ StudioControls.TextField {
         target: modelNodeBackend
         onSelectionToBeChanged: {
             if (__dirty && !writeValueManually) {
+                if (writeAsExpression)
+                    lineEdit.backendValue.expression = text
+                else
                     lineEdit.backendValue.value = text
             } else if (__dirty) {
                 commitData()
@@ -112,8 +116,12 @@ StudioControls.TextField {
         if (backendValue.isTranslated) {
            setTranslateExpression()
         } else {
-            if (lineEdit.backendValue.value !== text)
+            if (writeAsExpression) {
-                lineEdit.backendValue.value = text;
+                if (lineEdit.backendValue.expression !== text)
+                    lineEdit.backendValue.expression = text
+            } else if (lineEdit.backendValue.value !== text) {
+                lineEdit.backendValue.value = text
+            }
         }
         __dirty = false
     }