Unlike my earlier draft #664, this PR will not require DynamicProxy user code to set up any value converters for byref-like parameters.

Instead, any by-ref-like argument will automatically get substituted in IInvocation with a "reference" type:

• (削除) SpanArgument<T> (削除ここまで) (削除) SpanProxy<T> (削除ここまで) SpanReference<T> for Span<T> values
• (削除) ReadOnlySpanArgument<T> (削除ここまで) (削除) ReadOnlySpanProxy<T> (削除ここまで) ReadOnlySpanReference<T> for ReadOnlySpan<T> values
• (削除) ByRefLikeProxy (削除ここまで) ByRefLikeReference on .NET 8 for any non-span by-ref-like values
• (削除) ByRefLikeArgument<TByRefLike> (削除ここまで) (削除) ByRefLikeProxy<TByRefLike> (削除ここまで) ByRefLikeReference<TByRefLike> on .NET 9+ for any non-span by-ref-like values of type TByRefLike

Each of these (except the non-generic ByRefLikeReference) has a ref-returning Value property for accessing the actual value.

These class types are essentially references to the actual by-ref-like parameters. They use unmanaged pointers (void*) under the hood. I've added a big comment in the ByRefLikeReference.cs code file explaining why I think this is safe.

public interface IFoo
{
 void A(Span<char> characters);
 void B(ref Span<char> characters);
}
public void FooAInterceptor : IInterceptor
{
 public void Intercept(IInvocation invocation);
 {
 var charactersRef = invocation.Arguments[0] as SpanReference<char>;
 Span<char> characters = charactersRef.Value;
 }
}
public void FooBInterceptor : IInterceptor
{
 public void Intercept(IInvocation invocation);
 {
 var charactersRef = invocation.Arguments[0] as SpanReference<char>;
 Span<char> characters = charactersRef.Value;
 charactersRef.Value = characters[0..1]);
 }
}

I'm not quite done yet:

• add support for reading/writing by-ref-like argument values and propagating them through the interception pipeline
• add support for by-ref-like return values (as noted in a TODO in MethodWithInvocationGenerator.cs)
• update / replace unit tests in ByRefLikeTestCase (which still expect by-ref-like parameters to default / get nullified)
• write a documentation article on how to properly interact with by-ref-like arguments in IInvocation
• update ref/ contract files and the changelog

Will fix #651 and close #663 once completed and merged.