Blazor 6.0 migration guidance

[guardrex]

Fixes #23603
Addresses #22045

Artak ... TFM+packages per the current guidance at the top of the topic and it all ✨ Just Works!™ ✨.

I add a tidbit on how we recommend moving components+code to a new project to get ALL 6.0 features.

... and a handful of general updates to the whole topic ... mostly code-fencing to avoid loc on filenames and API.

[guardrex]

@Rick-Anderson ... I put up a bit on the NRT situation (angled for Blazor readers) at ...

https://docs.microsoft.com/en-us/aspnet/core/blazor/project-structure?view=aspnetcore-6.0#nullable-reference-types-nrts-and-net-compiler-null-state-static-analysis

Would you like me to place a modified (non-Blazor-y) copy of that section here at the end of the topic? If u prefer not to have a section here, I think devs would appreciate that link list on NRT subjects/guidance. If not a section, would you like those links in an Additional resources section? 👂

[Rick-Anderson]

Would you like me to place a modified (non-Blazor-y) copy of that section here at the end of the topic?

That would be great. @serpent5 can review/modify what you do.

[guardrex]

Ok ... great. I'll put that in here right now and ping back.

[guardrex]

@serpent5 ... I don't think that we'll end up waiting on Artak b/c he's probably buried in PU things ⛰️⛏️. This topic is sure to get a final PU 👁️ later, so we can go ahead with final review for these nits and bits now. I'll merge after making your suggested updates.

[serpent5]

Just a few minor suggestions. I don't expect that you'll take them all, but I'm hoping to learn something in the process.

[guardrex]

@serpent5 ... Ok ... try it now. We might need to touch any of those spots again on this PR, and/or you can pass the whole doc again with another PR as needed for further updates. I don't care if anything gets revised back or changes to anything else. All of my changes are more of the suggestion variety, usually based on consistency with prior decisions around the repo that might not make sense here.

[serpent5]

This looks really good. I think the bulleted FAQs approach works well.

[guardrex]

Ok ... let's go ahead. I'll merge this now, and I'm sure it will get further work as we go. It happens every release. We just try to be careful to avoid 😈 Merge Conflict Grimlins 😈.

I'm going to go provide that What's New for Blazor piece as an issue comment.

btw --- I asked Dan about where to place the NRT section ... here or over in What's New content. He didn't respond tho (yet). He might want it moved. If I hear on a Blazor issue, I'll signal you if that's the case if there's an open PR for this topic. Otherwise, I'll move it quickly 🏃 if he makes the request to do so.