docs: fix the routing guide examples - #71412

Several examples and statements in the routing guides do not match the
router.

The redirect function example in the redirecting routes guide has no
`pathMatch`. With the default `prefix`, `restaurant/:location/menu` also
matches the destination URLs the page defines, such as
`restaurant/downtown/menu/lunch`, and the leftover segment is appended to
the redirect result. Add `pathMatch: 'full'`.

The `CustomRouteReuseStrategy` example passes `handle: DetachedRouteHandle |
null` into a `Map<Route, DetachedRouteHandle>`, which does not compile under
strict mode. Guard the `set` call with `if (handle)`.

The resolver guide says the data comes from the snapshot using `signal`, but
the example uses `toSignal` on the `data` observable. Three snippets in the
read route state and outlet guides use `inject` or `Signal` without
importing them, and `userId` is `string | null` because `paramMap.get()`
returns `null`. The URL matcher guide says the page shows `Hello, Angular!`,
but the example template renders `Hello Angular!`. The `canActivateChild`
guard runs once for each child route being activated, so "once for each of
them" replaces "once for both components".