Always show down arrow regardless of expanded state

This is something our UX designer wants to change for all expandable header bar menus. The down arrow indicates that something will pop-up downwards once clicked. It is unnecessary to feedback the state of the expansion in the icon.

Contributes to CURA-8008.

resources/qml/ExpandableComponent.qml

@@ -167,7 +167,7 @@ Item
                     verticalCenter: parent.verticalCenter
                     margins: background.padding
                 }
-                source: expanded ? UM.Theme.getIcon("ChevronSingleDown") : UM.Theme.getIcon("ChevronSingleLeft")
+                source: UM.Theme.getIcon("ChevronSingleDown")
                 visible: source != ""
                 width: UM.Theme.getSize("standard_arrow").width
                 height: UM.Theme.getSize("standard_arrow").height

resources/qml/ExpandablePopup.qml

@@ -180,7 +180,7 @@ Item
                     verticalCenter: parent.verticalCenter
                     margins: background.padding
                 }
-                source: expanded ? UM.Theme.getIcon("ChevronSingleDown") : UM.Theme.getIcon("ChevronSingleLeft")
+                source: UM.Theme.getIcon("ChevronSingleDown")
                 visible: source != ""
                 width: UM.Theme.getSize("standard_arrow").width
                 height: UM.Theme.getSize("standard_arrow").height