Guidance for error handling in Blazor

[SteveSandersonMS]

This is part of #10472

Enumerate all the places we'd expect a developer to write some manual error handling code so we can document and explain them.

With respect to the different boundaries between framework and application code (lifecycle
methods, event handlers, dispose, DI services, rendering, etc.), which of them will terminate the circuit if there's an exception? Which of them will surface the error in a way that naturally appears to the user and/or gets logged?

The overall outcome here should be some info that can be the basis for documentation. And if necessary, tweak product code to improve anything that seems wrong about the built-in behavior.

[SteveSandersonMS]

OK, the draft content and doc proposal is now done at dotnet/AspNetCore.Docs#13288. Since this has now become a docs issue, I'll close this as done here.