Scanner wedge mode (#437)

* Add code_scan_listener package

* Implement wedge controller widget

* Update barcode settings widget

- Allow user to choose which barcode scanner to use

* Fix typo

* Select barcode scanner widget based on user preference

* Fix rendering issues for wedge controller

* Update release notes

* Add unit test for wedge scanner widget

- Required some tweaks to other code

* Use better library

- https://github.com/fuadreza/flutter_barcode_listener
- Fork of https://github.com/shaxxx/flutter_barcode_listener
- Properly handles key "case" issues (shift, essentially)
- Verified that it works correctly for multiple character types

* Local copy of code, rather than relying on package which is not available on pub.dev

* Fix unit test

lib/barcode/controller.dart

@@ -58,9 +58,9 @@ class InvenTreeBarcodeControllerState extends State<InvenTreeBarcodeController>
       processingBarcode = true;
     });
 
-    BuildContext? context = OneContext().context;
+    BuildContext? context = OneContext.hasContext ? OneContext().context : null;
 
-    showLoadingOverlay(context!);
+    showLoadingOverlay(context);
     await pauseScan();
 
     await widget.handler.processBarcode(data);