Mismatch in keeping interfaces with explicit implementation

[MichalStrehovsky]

Reported in dotnet/runtime#40582.

I'm working on this right now, just filing an issue for tracking.

Simplified repro without regex:

    interface IFoo<T>
    {
        void Frob();
    }

    class Foo : IBar, IFoo<string>, IFoo<object>
    {
        void IFoo<string>.Frob()
        {   
        }

        void IFoo<object>.Frob()
        {
        }

        public void Bork()
        {
        }
    }

    interface IBar : IFoo<object>
    {
        void Bork();
    }

    class Bar : IBar
    {
        public void Bork()
        {
        }

        public void Frob()
        {
        }
    }

    class Program
    {
        static Foo f;

        static void Main(string[] args)
        {
            ((IBar)new Bar()).Bork();

            if (f != null)
                ((IFoo<object>)f).Frob();
        }
    }

Results in:

Unhandled exception. System.TypeLoadException: Type 'cns.Foo' from assembly 'cns, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' tried to override method 'cns.IFoo<System.String>.Frob' but does not implement or inherit that method.
   at cns.Program.Main(String[] args)