* refactor: refactor router-view + fix keep-alive route guard this context

* test: add skipped unit test for keep alive

* refactor(e2e): omit props in v-slot

* test(e2e): add guard tests keep alive

* test(e2e): fix keep alive test

* refactor(router-view): render slot content if empty

Co-authored-by: Eduardo San Martin Morote <[email protected]>

Close #346

BREAKING CHANGE: HistoryLocation is just a string now. It was pretty much an
internal property but it could be used inside `history.state`. It used to be an
object `{ fullPath: '/the-url' }`. And it's now just the `fullPath` property.

BREAKING CHANGE: the history property was marked as internal already. Since we
need to pass the history instance to the router, we always have access to it,
differently from Vue Router 3 where the history was instantiated internally.
The history API was also internal (it wasn't documented), so this change
shouldn't be a problem as people shouldn't be relying on `router.history` in
their apps. If you think this property is needed, please open an issue to
discuss the use case. Note it's already accessible as you have to create it:
```js
export const history = createWebHistory()
export const router = createRouter({ history, routes: [] })
```