Share warning codes with roslyn analyzers

[sbomer]

Some of the analysis we want to do can be done either in a Roslyn analyzer or in the linker. The plan is for these to share warning codes, so that a given warning can be disabled for both Roslyn and linker analyzers via NoWarn, etc.

Ideally we would share some of the analysis infrastructure and warnings to begin with - but in the meantime, we should avoid using the following codes for other linker warnings.

Introduced by https://github.com/dotnet/roslyn-analyzers/pull/3921/files:

• IL3000: System.Reflection.Assembly.Location' always returns an empty string for assemblies embedded in a single-file app. If the path to the app directory is needed, consider calling 'System.AppContext.BaseDirectory'.
• IL3001: Assemblies embedded in a single-file app cannot have additional files in the manifest.