Disable package API validation for .NET tools

[baronfel]

Fixes #50755

.NET Tools don't expose APIs and so should not participate in API baseline validation.

[ViktorHofer]

@baronfel EnablePackageValidation=true is an opt-in experience so it doesn't run by default. Is the intention of this change to override a user setting? If so, a refinement of this condition here might make more sense:

sdk/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ApiCompat.ValidatePackage.targets

Line 26 in dfa14d7

Condition="'$(EnablePackageValidation)' == 'true' and '$(IsPackable)' == 'true'">

[baronfel]

yeah, we do intend to override a user setting - it's never correct for Tools to do package validation IMO. Architecturally, I want to keep the validation targets ignorant of tools - they are doing the correct thing by providing knobs, it's up to the specific feature/experiences to use those knobs to deliver the desired experience.