Add Blazor content to the 9.0 Migration article

### Description

There's at least one item to call out, possibly more.

### Page URL

https://learn.microsoft.com/en-us/aspnet/core/migration/80-90?view=aspnetcore-8.0&tabs=visual-studio#blazor

### Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/migration/80-90.md

### Document ID

ff7b9e49-f8a8-552a-e27e-c604c858b318

### Article author

&mdash;