Fix Router Config Issues #4300 (go_router_builder/example) (#4369)
This PR is an extension of the previous PR #4300 that I submitted. The previous PR, being based on the main branch, was closed and the contents were copied to a new branch in order to make further contributions.ð
In the previous PR, an assertion error was fixed by adding routeInformationProvider to MaterialApp.router. After a series of code reviews, we updated to use routerConfig and added some test codes.
All the contents have been transferred to the current bugfix/RouterConfig branch.
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