Move base hovered logic out of ComboBox.qml since base is undefined in most places the component is used.

CURA-9424

plugins/PerObjectSettingsTool/PerObjectSettingsPanel.qml

@@ -150,6 +150,7 @@ Item
             width: parent.width / 2 - UM.Theme.getSize("default_margin").width
             height: UM.Theme.getSize("setting_control").height
             textRole: "text"
+            forceHighlight: base.hovered
 
             model: ListModel
             {

resources/qml/Settings/SettingComboBox.qml

@@ -18,6 +18,7 @@ SettingItem
 
         model: definition.options
         textRole: "value"
+        forceHighlight: base.hovered
 
         anchors.fill: parent
 

resources/qml/Settings/SettingExtruder.qml

@@ -17,6 +17,8 @@ SettingItem
         id: control
         anchors.fill: parent
 
+        forceHighlight: base.hovered
+
         property var extrudersModel: CuraApplication.getExtrudersModel()
 
         model: extrudersModel

resources/qml/Settings/SettingOptionalExtruder.qml

@@ -23,6 +23,7 @@ SettingItem
     {
         id: control
         anchors.fill: parent
+        forceHighlight: base.hovered
 
         model: base.extrudersWithOptionalModel
 

resources/qml/Widgets/ComboBox.qml

@@ -19,6 +19,7 @@ ComboBox
     property var defaultTextOnEmptyIndex: ""  // Text displayed in the combobox when the model has items but no item is selected
     property alias textFormat: contentLabel.textFormat
     property alias backgroundColor: background.color
+    property bool forceHighlight: false
 
     enabled: delegateModel.count > 0
 
@@ -46,7 +47,7 @@ ComboBox
         State
         {
             name: "highlighted"
-            when: ((base != undefined && base.hovered) || control.hovered) && !control.activeFocus
+            when: (control.hovered && !control.activeFocus) || forceHighlight
             PropertyChanges
             {
                 target: background