QmlDesigner: Disable fill type outside base state

Disable fill type ComboBox in ColorEditor when not in base state. Add
tool tip to make user aware.

Task-number: QDS-6184
Change-Id: Iee5644fff16fe93f2090e1cb117e96bb436fe1dd
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

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

@@ -386,6 +386,7 @@ SecondColumnLayout {
 
                             property ListModel items: ListModel {}
 
+                            enabled: isBaseState
                             implicitWidth: StudioTheme.Values.colorEditorPopupCmoboBoxWidth
                             width: implicitWidth
                             actionIndicatorVisible: false
@@ -442,6 +443,13 @@ SecondColumnLayout {
                                 }
                                 colorEditor.updateThumbnail()
                             }
+
+                            ToolTipArea {
+                                enabled: !isBaseState
+                                anchors.fill: parent
+                                tooltip: qsTr("Fill type can only be changed in base state.")
+                                z: 10
+                            }
                         }
 
                         ExpandingSpacer {}