IDISP025 doesn't emit with IAsyncDisposable

[Kuinox]

IDISP025: Class with no virtual dispose method should be sealed

public class Diposable : IDisposable // IDISP025: Class with no virtual dispose method should be sealed
{
    public void Dispose()
    {
    }
}

public class AsyncDiposable : IAsyncDisposable // Nothing.
{
    public ValueTask DisposeAsync()
    {
        return new ValueTask();
    }
}

AFAIK there is no reason for not emitting this warning on AsyncDisposable.

[JohanLarsson]

Agreed analyzer should nag for consistency.
This may be an easy fix, could be analyzer code that is somewhat sane but could also be normal code.

[sorensenmatias]

I created a PR for this: #416