[Infrastructure] We should add APICompat checks against previous shipped version of the assemblies to detect breaking changes

Currently we aren't running baseline package validation in our builds because we drop older TFMs which makes us run into https://github.com/dotnet/sdk/issues/48602 and therefore we are not detecting breaking changes as part of the build. This issue is tracking us enabling checks such that we know at build time whether or not a change is breaking when compared against the previously shipped version of that asset.

cc: @wtgodbe