Add Extended messages data to binary log

[rokonec]

Fixes #9091

Context

We have introducing new extended event args (error, warn, message, custom) so time ago.
This PR is about logging extended data into binary log and will serve for modifying bin log viewer as well.

Changes Made

Add BuildEventArgsFieldFlags.Extended and implement related code.

Testing

Unit tests

Notes

[rokonec]

@KirillOsenkov I suppose we shall 1st release forward compatible log viewer. We can do it in two phases:

1. make it read new file version
2. UI changes to somehow show extended data

While I can easily do 1 for 2 I might need some help.
We expect that after C++ teams implement extended error logs people might start to need it frequently.

[KirillOsenkov]

Do we have a design document or a wiki page outlining the problem space, the motivation and the proposed approach? What do we know about the existing usage of the "exotic" event args? Do we have a list of teams/scenarios depending on these?

As we discover scenarios and knowledge, let's add to the doc. I'm sure we'll break someone, so would be nice to point them to the doc. I've always felt uncertainty about the exotic event args - they're ancient and it's unclear who if anyone is still using them and for what. Would also help to know these scenarios so we can test and validate.

[rokonec]

@KirillOsenkov

Research of usage custom event arguments was concluded in:
#8825

Custom event arguments has been deprecated for dotnet core msbuild in favor of new messages containing general purpose transparent payload. See #8917

I would not care too much about binlog supporting rare needs for custom events args.
However, for close future, C++ team is improving VS with enhanced structured errors and warnings info json format called SARIF. These structured data comes from C++ compiler.

We believe, that there can be substantial value in capturing and showing such info in log viewer. And this PR is the part of such effort.

[KirillOsenkov]

Sounds good. I'm missing a ton of context, but superficially everything seems fine.

See if you can utilize BuildEventArgsFieldFlags in any way:
https://source.dot.net/#Microsoft.Build/Logging/BinaryLogger/BuildEventArgsFieldFlags.cs,58948e4bf96933c9,references

Perhaps you can avoid writing a boolean to see if extended data is present if you can write a single bit in the flags.

[rokonec]

@KirillOsenkov I have totally missed BuildEventArgsFieldFlags. Have just simplified and rewritten it. Good catch. Thx

[rokonec]

It is ready for review. I just left it in Draft so it is not merged before we release compatible log viewer.

[JanKrivanek]

Looks good!

[KirillOsenkov]

Looks OK as far as I can see