Opt into IEventSource4

[KirillOsenkov]

This is similar to #23249

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[dsplaisted]

Looks good, but shouldn't this flow to main via normal codeflow anyway?

[rainersigwald]

There are two loggers here. While working on #23249 I discovered that this one didn't need to change, but that is surprising and when @KirillOsenkov asked about it offline I started wondering whether it was because of dotnet/msbuild#7219. It's at worst harmless to opt both in, so I support this change. However, I think the right place for it might be release/6.0.3xx so it ships sooner than .NET 7.

[KirillOsenkov]

Could one of you please retarget to the right branch?

[dsplaisted]

Could one of you please retarget to the right branch?

@KirillOsenkov I've done so, but now it's bringing a whole bunch of commits from main. You'll need to rebase locally and force push I think.

[KirillOsenkov]

Done, thanks