Improve AdditionalAssemblies coverage

[guardrex]

Fixes #31081
Addresses #28161

We'll need coverage on static versus interactive routers.

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Internal previews

📄 File	🔗 Preview link
aspnetcore/blazor/components/render-modes.md	ASP.NET Core Blazor render modes
aspnetcore/blazor/fundamentals/routing.md	ASP.NET Core Blazor routing and navigation
aspnetcore/migration/70-80.md	[Visual Studio Code](https://review.learn.microsoft.com/en-us/aspnet/core/migration/70-80?branch=pr-en-us-31131)

[danroth27]

This looks good to me.

[guardrex]

@MackinnonBuck ... Your explanation unlocked a couple of concepts. Your text might be further organized by static versus interactive routing. I'm feel'in that I might still have a 😈 or two, but see if what's on the PR now breaks it down clearly for readers.

Also, I think it is good to leave the static/interactive discussion here in this section. These concepts are a bit complicated. However, I'd still like to add something general on the static/interactive routing concepts near the top of the article. I'm going to try and do that now.

[guardrex]

@MackinnonBuck ... I added content at the top of the article on static/interactive routing to at least get the ball rolling on review. I probably don't have it exactly right, but you can see what I think readers (and a silly 🦖) will need to understand.

I took my BWA test app (global Interactive Auto rendering applied, Routes component in the .Client project), and I dropped an Interactive Server component into the server project. Indeed!!! When I navigated to the test component, it briefly appeared in the UI under static routing before landing on a 404 when interactive client-side routing took over.

UPDATE: The latest commit calls this section out in the Migration guidance.