[Blazor] Lazy loading improvements for Webassembly

[javiercn]

• With prerendering, it can happen that we prerender a path that requires lazy loaded assemblies to render. The current APIs don't offer a way to make sure those assemblies are loaded before the page tries to render, which results in failures when the app goes interactive. We need:
• A LazyAssemblyLoader implementation for prerendering (if you try to do this on any current .NET version it will fail).
• A way to run the lazy loading logic before we try to render the page in webassembly.

Alternatively, can the runtime provide a way to handle lazy loading assemblies

[sbwalker]

@javiercn one of the biggest challenges I have with lazy loading is related to service registration. Blazor client assemblies often contain service classes for interaction with the back-end APIs (ie. service classes per domain which abstract the details of the endpoints, serialization, auth, etc... and uses HttpClient internally to return strongly typed data). This approach relies on .NET dependency injection.... which means these services need to be registered in the service container. However, .NET only allows services to registered during startup - which makes it impossible to use a lazy loading approach with these assemblies. The only "solution" is to abandon dependency injection and instantiate service classes manually - or avoid service classes altogether and use HttpClient in your components – or split your client services classes into a separate project/assembly from your client components... none of which are optimal.