Method cannot be `virtual` when the type is generated as a struct

[ArcturusZhang]

This code cannot compile:

public readonly struct Foo
{
    protected virtual void WriteCore() {}
}

It should be:

public readonly struct Foo
{
    private void WriteCore() {}
}

if we want to keep this method, or generate it inline.

[m-nash]

@JoshLove-msft can you verify if this affects OAI.

[JoshLove-msft]

Yes, there are numerous structs in OAI.