Add documentation for AssemblyMetadata item

[kzu]

Documents the new behavior in dotnet/sdk#3440

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[PRMerger18]

@kzu : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[Mikejo5000]

@rainersigwald for review

[rainersigwald]

Looks ok to me. Two concerns:

• This functionality is not yet merged, so it doesn't work anywhere (yet!)
• No mention of what release the functionality is (will be) added in, or that it only works in Microsoft.NET.Sdk projects.

Not sure what the usual docs procedure for such a situation is . . .

cc @livarcocc since Peter has moved on

[Mikejo5000]

For these scenarios, we would need to say something like "Starting in MSBuild <version>, ...."

For SDK-only information, it's critical to mention that or the doc messaging will start to get confusing.

[kzu]

Hm... I'm not so sure that page is the right place for this doc... It starts by saying:

In MSBuild, an item is a named reference to one or more files.

But these items (AssemblyMetadata but also #3937 for InternalsVisibleTo) are just metadata, not files. Also, in order to properly document them, I'd need to talk about the assembly info codegen that happens only on SDK-style, and the associated properties that affect that generation. And that would no longer belong to a "Items" discussion.

So maybe what we need is an entirely new document talking about AssemblyInfo codegen in general, what properties and items affect it and how? If we agree that's the better way, I'll close the other docs PR and unify on just one.

[Mikejo5000]

@rainersigwald for input

[rainersigwald]

I think having a link to SDK docs (possibly not-currently-existing, cc @mairaw) would be reasonable, but I worry about smearing things out into too many places, so I think this is a good place too.

Saying items are files is flat wrong and we should just remove that sentence.

[Mikejo5000]

@kzu Daniel, could you commit the suggestion? Then we can merge. Thanks!

[PRMerger6]

@kzu : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[kzu]

done @Mikejo5000

[Mikejo5000]

Thanks!

[Mikejo5000]

#sign-off