Fix another back button issue

[micahmo]

Pull Request Description

This PR fixes another broken issue from #1251 and related to #1260. In the latter PR, I fixed some issues where the top-level back button handler tries to take precedence even when it's not at the top of the navigation stack. However, there's another case -- the profile page for the logged-in user -- where the back button handler technically is at the top of the navigation stack, but it still needs to defer to the back button handler on the user page. It looks like the easiest solution here is to disable the top-level handler when we're on the account page and let the account page handle scrolling to the main page via a delegate. Let me know if you agree!

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Before

https://github.com/thunder-app/thunder/assets/7417301/af520c4b-503d-4f2a-9c3f-69284a2cecda

After

https://github.com/thunder-app/thunder/assets/7417301/25cb604a-3a7e-4f6d-b4cb-3e7ab8053514

Checklist

• [ ] Did you update CHANGELOG.md?
• [ ] Did you use localized strings where applicable?
• [ ] Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

I think there's a simpler way to achieve this behaviour without having to pass in callback functions.

We can use stopDefaultButtonEvent to determine if we should run a given BackButtonInterceptor handler.

// thunder_page.dart
FutureOr<bool> _handleBackButtonPress(bool stopDefaultButtonEvent, RouteInfo info) async {
  final bool topOfNavigationStack = ModalRoute.of(context)?.isCurrent ?? false;

  if (!topOfNavigationStack) return false;
  if (stopDefaultButtonEvent) return false; // Add this line

  // ... rest of code
}

Adding this seems to give the desired behaviour. Let me know if this change works! I made a quick PR with this change: https://github.com/thunder-app/thunder/pull/1293

[micahmo]

Yeah that's perfect, thanks! 😄

[hjiangsu]

If it works, I'll go ahead and close this PR in favour of the other one!