[go_router] remove navigatorBuilder, GoRouterRefreshStream, and urlPathStrategy

[chunhtai]

fixes https://github.com/flutter/flutter/issues/108145 fixes https://github.com/flutter/flutter/issues/108128 fixes https://github.com/flutter/flutter/issues/108132

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[flutter-dashboard[bot]]

This pull request was opened against a branch other than main. Since Flutter pull requests should not normally be opened against branches other than main, I have changed the base to main. If this was intended, you may modify the base back to go_router_v5. See the Release Process for information about how other branches get updated.

Reviewers: Use caution before merging pull requests to branches other than main, unless this is an intentional hotfix/cherrypick.