Bump PackageValidation against 9.5.0 and enable for stable MEAI packages

[joperezr]

FYI: @stephentoub@jeffhandley this is turning on package validation for MEAI and MEAI.Abstractions to protect against unintentional breaking changes.

Microsoft Reviewers: Open in CodeFlow

[joperezr]

@shyamnamboodiripad also enabling it for MEAI.Evaluation packages.

[jeffhandley]

Thanks, @joperezr; you beat me to it!

I was going to ask you and @RussKie about package validation and ApiChief. They are both used in this repository, but I was previously unfamiliar with ApiChief. I got the impression ApiChief as an additional layer of guardrails above and beyond whta the .NET API Compat tool provides. Is it correct that both are in use in this repo?

[shyamnamboodiripad]

Thank you!

[RussKie]

ApiChef is an inhouse tool built by the R9 team. I'm not too familiar with it, but I think it serves as an alternative to the Roslyn's public API analysers. One of the key features it was addressing was the warnings for the use of experimental API.

Few years ago, I made an attempt to replace it with the Roslyn analysers, but back then those had no experimental API support; so, I had to roll the change back. AFAIU, the analyzers now have support for the experimental attribute, so maybe it's time to re-evaluate the usefulness of the ApiChef?