perf(guard): Add a tool function to handle the logic of TargetRouterV…

[LockingReal]

When I'm trying to solve a recent issue (to better understand vue-router), I see here, and I think I can pull out a function to improve it,......and,flow check, It makes me feel uncomfortable 🤣

I don't think my modification will cause e2e-test error (⊙﹏⊙) @posva

[netlify[bot]]

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