GlobalToolBar: Clean up, fix and rework BreadcrumbControl
Ports everything to qualified property access. Shuffles properties and adds helper functions as needed. Ports Flickable to ListView. Fixes RTL positioning. ListView is quite weird is how it treats contentX in RTL mode, but now it works. Fixes various JavaScript and QML gotchas, like executing long-running handler in a broken/deleted context of a delegate; or inappropriate abuse of children list for get currentItem from a Repeater. Fixes off-by-one error in handling clicks in layers mode. --- Test plan: 1. Run Kirigami Gallery in both English and RTL locales. 2. Open sidebar, select «Top Bar Style…» -> Select «Breadcrumb». 3. Open sidebar again, select «Open a Layer». 4. On layers page, push couple of layers with a button. 5. Resize window back and forth to test behavior with different width values.