APICompat should compare relevant assembly-level attributes

[ericstj]

APICompat doesn't catch when an assembly removes CLSCompliant.

It also doesn't check for other top level attributes like AllowPartiallyTrustedCallers etc that might impact usage.

We should consider opting-in a set of assembly level attributes, or maybe comparing all assembly level attributes with a few built in exclusions.

See dotnet/maintenance-packages#134

[dotnet-policy-service]

@dotnet/area-infrastructure-libraries a new issue has been filed in the ApiCompat area, please triage