Cannot control generated [Query] accessibility

[LilithSilver]

Problem

Currently, all methods generated with [Query] are, by default, public, regardless of the accessibility of the method.

This causes several problems:

• Private, class-local types cannot be used in a query method header, even if the method is only called within the system. For example, if a private struct SomeLocalInfo {} is defined within the BaseSystem, that can never be used as a [Data] parameter within a query without exposing it to the public.
• Systems can never be public in a module, unless you want all your queries to be exposed to the public API. Instead, a module must manually wrap all systems and make all systems internal (extremely bad, if you're making a game engine with drop-in systems!)

Solution

Instead, provide a parameter to the [Query] attribute:

public enum QueryAccessibility
{
    CopyMethod, // copy the source method's accessibility
    // fill in attributes from  Microsoft.CodeAnalysis.Accessibility
}

public class QueryAttribute : Attribute
{
    QueryAccessibility Accessibility = QueryAccessibility.CopyMethod;
}

By default, the query could either be public, or copy the source method's accessibility, depending on whether it's super important to maintain API.