Generalize Blazor NRT and null-state analysis content for all ASP.NET Core templates

[danroth27]

There's a nice section in the Blazor docs about the enabled null-state analysis in the templates, but this isn't really a Blazor specific feature. We did this for all ASP.NET Core templates in .NET 6. The content should be generalized to not be Blazor specific.

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Document Details

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• ID: d31248d7-d2c2-1a17-3173-889a0d9bb6e8
• Version Independent ID: 6f27ff37-6b3a-57f5-353a-5cf5aabba7cf
• Content: ASP.NET Core Blazor project structure
• Content Source: aspnetcore/blazor/project-structure.md
• Product: aspnet-core
• Technology: aspnetcore-blazor
• GitHub Login: @guardrex
• Microsoft Alias: riande

[guardrex]

It was placed in the Migration topic on #23607. I'll remove it here now.

[guardrex]

Done! ... If it's preferred for What's New and not the Migration topic, I'm 👂 here or on #22852. I'll move it off of the PR at #23607 and supply it to Rick/Kirk on the What's New issue. 👂