3932 Move integration test to null safety for multiple plugins (cla: yes, p: webview_flutter, p: image_picker, p: in_app_purchase, p: wifi_info_flutter, p: quick_actions, p: connectivity, p: device_info, platform-ios, platform-android, platform-macos)

3944 [in_app_purchase] Added support to request list of purchases (cla: yes, p: in_app_purchase, platform-android)

3945 [in_app_purchase] Add “Restore purchases” button to example App (cla: yes, waiting for tree to go green, p: in_app_purchase)

3950 [in_app_purchase_ios] Add Restore purchases button to example (cla: yes, p: in_app_purchase, platform-ios)