[Blazor] Inject different services during prerendering

[Andrzej-W]

I don't know if prerendering already works in Blazor 0.9 on WebAssembly but we should be able to use different services during prerendering and in the client app. The most obvious example:

• during prerendering we can use direct database access to read information
• in the client app we have to use WebAPI calls

I would like to create a common interface (repository pattern) and two different implementations to optimize server performance.

There is an issue related to prerendering and JSInterop already filled in: #8404 Maybe both problems can be solved at the same time.

[SteveSandersonMS]

You can already use different DI services during server-side execution (e.g., prerendering) vs client-side execution. By default you already get two different Startup.cs classes, so just put whichever services you want in each.

We're not planning to have an entirely separate DI container for prerendering vs other server-side execution, as that wouldn't make sense given that the same component instances will have a lifetime spanning both prerendering and then ongoing server-side execution.