backport navigation guard return values

[1593292349]

What problem does this feature solve?

being able to return a value in a navigaiton guard:

router.beforeEach(to => {
  if (!user)
  return { name: 'login', query: { redirectTo: to.fullPath } }
})

### What does the proposed API look like?
Like v4. X

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[posva]

Some features cannot be backported without rewriting big parts of the router. I tried porting back as much as I could in the limited time I have.

If anybody wants to backport the navigation guard return value, that would be nice