Consider emitting GeneratedCodeAttribute on all generated types

[AArnott]

See the docs for the attribute. The LibraryImportAttribute source generator emits code that uses this. It seems like a possibly good idea.

[elachlan]

The GeneratedCodeAttribute doesn't have AllowMultiple, so it can only be applied to a single file of a partial class/struct. This seems super weird since I would imagine you want to tag each code file with the attribute.
https://docs.microsoft.com/en-us/dotnet/api/system.codedom.compiler.generatedcodeattribute?view=net-6.0