Proj0006: Add additional files to improve static code analysis

.NET project file analyzers need access to files that are not available via the analyzer context. By adding additional non-compiling files, those files become available in the analyzer context too.

The project file that is being analyzed, the Directory.Build.props, Directory.Build.target, Directory.Packages.props,*.resx, *.props, and *.targets, are automatically are added by the .NET project files. Files that are analyzed but not included automatically (this could be an <Import> statement) should be included manually.

Compliant

To include a file that is not yet added as additional file:

<Project Sdk="Microsoft.NET.Sdk">

  <ItemGroup>
    <AdditionalFiles Include="{file.to.include}" `Visible="false"` />
  </ItemGroup>

</Project>

Note that - if preferred - the visibility can be omitted. In that case, the file will might show up in the IDE.