Slightly adjust width of button

This is more in line with what you see, so you can click on the icon properly to open the per-object settings panel. And the text gets properly elided where the icon starts.

resources/qml/ObjectItemButton.qml

@@ -85,7 +85,7 @@ Button
                 right: parent.right
                 rightMargin: 0
             }
-            width: childrenRect.width
+            width: contentItem.width
             height: parent.height
             padding: 0
             leftPadding: UM.Theme.getSize("thin_margin").width