[go_router] Fix replace routes hanging the originating completer

[nouvist]

The behavior of replace and pushReplacement involves popping the last route and ignoring the completer, leaving the last route's future unresolved. This PR introduces new behavior for both methods to inherit the last route's completer if the last route is an ImperativeRouteMatch.

Expected issue(s) should be fixed by this:

• Awaiting a GoRoute.push() is not resolving when the push page gets replaced via pushReplacement flutter#141251

Previous behavior:

sebelum.mp4

This PR behavior:

sesudah.mp4

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[ikurek]

@nouvist LGTM, thank you for submitting the fix, I was facing the same issue

[chunhtai]

What if the type T mismatched for the new route and the old route. Instead of inherited the completer, I think it should resolve the previous route's future because it is replaced.

[nouvist]

Yeah, that's the problem, but I still think resolve the completer when the replacement pops up is my preferred, as the waiting route can hold until its screen reappears.

I propose, what if the push (etc) had a mapReplacementResult? But it may need to be on RouteInformationState and ImperativeRouteMatch, which I'm not sure if there will be breaking changes or not.

[chunhtai]

This feels weird, If we want to separate two use cases.

1. resolve the result immediately in pushReplacement
2. replace the future in pushReplacement.

I think we should make two different API, maybe a pushReplacement for (1) and a pushReplaceResultFuture for (2), and in (2) we should force the type to be the same as previously pushed route.

[nouvist]

case (2) that match its originating type is guaranteed. this implementation makes the caller of the originating route is the one who's responsible for replacing future. for example, A is the one that responsible for replacing C result to match with B result type when it's pushing B. that's why mapReplacementResult is required for each pushed new route, because the assumption is any route can be replaced.

Route A -- (pushing) --> Route B -- (replaced by) --> Route C

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I do consider to make the replace and pushReplacement itself that responsible for replacing future. but I struggle to make it match the originating route type. I think it's similar to pop where we have no idea what type it should be.

I didn't consider case (1) before, it is indeed necessary to implement. but then, when routes can be resolve immediately when replaced, it needs value to return, and then again, we have no idea what type it should be, like pop is.