Consider using back_button_interceptor

[flodaniel]

Is your feature request related to a problem? Please describe.

Currently flow_builder implementation has a conflict with packages that use the back_button_interceptor package, because both use the method SystemChannels.navigation.setMethodCallHandler to listen to navigation events. This causes the onGeneratePages callback to no longer being called on android back button navigation in certain scenarios.

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As the implementation of back_button_interceptor is lightweight and stable (nearly no open issues, version 6), I propose using it instead of relying on the own interceptor implementation. This resolves any conflicts and results in less code to maintain for flow_builder.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
Sadly, I was unable to find a solution to merge to calls to the SystemChannels.navigation.setMethodCallHandler API. If that is somehow possible, this would also be a viable option.

Additional context
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I discovered the bug when working with the loader_overlay package. Initially I filled a bug report there. After discovering the conflict, I filled a bug report with back_button_interceptor here. The maintainer confirmed the conflict, but declined to work on a possible solution, as they are not using flow_builder.

[chillbrodev]

@felangel We really need a fix for this as it is impacting usage of FlowBuiler on Flutter Web. We can see that the MethodCall of pushRouteInformation is being swallowed by the _handleSystemNavigation function. This prevents navigation from working when utilizing GoRouter

[RootSoft]

@felangel Having the exact same issue with using go_router and deep linking.
As soon as I open a screen that uses flow_builder, deep linking stops works because flow_builder overrides the system navigation.

[anqit]

I'm not sure if this is the best issue to pile this on, but I would love to use this package (specifically wizard_router) for certain areas of an app while using go_router as the main navigation, but it has been difficult to get the two to play nicely with each other.