Add navGraphViewModel delegate support

[haroldadmin]

Is your feature request related to a problem? Please describe.
The Navigation Architecture Component supports scoping ViewModels to a Navigation Graph. These ViewModels can be instantiated using by navGraphViewModels(<nav-graph-id>) delegate. Add support for this delegate to Vector too.

Describe the solution you'd like
Add a separate vector-nav-ext module and add support for this delegate in there.

Describe alternatives you've considered
A completely custom solution to allow scoping ViewModels to an arbitrary scope, but this will take a lot of time to implement.