Consider running Publish target when _IsPublishing is true

[sbomer]

For folks who don't use dotnet publish, it's a common pattern to inject the Publish target so that they can run msbuild without specifying /t:Publish. See examples from #37872 (comment):

Lots of people do that, some of them even pass _IsPublishing but most of them just do some variation of "run the Publish target". Here is a popular pattern (note these are all pretty high profile).

This won't fully replicate the effects of dotnet publish unless they also pass -p:_IsPublishing=true. Would it make sense to run the Publish target after Build when _IsPublishing is set, so that folks using msbuild can at least do msbuild -p:_IsPublishing=true and get the same output as dotnet publish? (We wouldn't advertise that until it's made public, see #26324)

@MichalStrehovsky @rainersigwald @marcpopMSFT @dsplaisted @agocke

[dotnet-issue-labeler]

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