Fix DynamicProxyException ("duplicate element") due to DynamicProxy not accounting for outer type names of nested types

[JelleKerkstra]

This PR resolves the DynamicProxyException Duplicate element: Castle.DynamicProxy.Generators.MetaMethod when generating a proxy that implements the following interfaces due to the nested classes.
In the current implementation, only the namespace, type name and method name are considered. In this PR, the declaring type names are also used when generating explicit interface implementations due to matching method names.

public static class OuterWrapper
{
	public static class InnerWrapperA
	{
		public interface ISharedName
		{
			void M();
		}
	}

	public static class InnerWrapperB
	{
		public interface ISharedName
		{
			void M();
		}
	}

	public static class InnerWrapperC
	{
		public interface ISharedName
		{
			void M();
		}
	}
}

[stakx]

@JelleKerkstra, apologies for the very long delay. I realise it has been more than a year since you submitted this PR. If you're no longer interested in this, that's OK, too. Let me know whether or not you'd like to proceed.

[stakx]

@JelleKerkstra, I haven't heard back from you, but I'd like to see this bug fix get merged. Since there was an issue in your proposed code changes with the fast path getting removed from SwitchToExplicitImplementationName, I added a few commits of my own to your PR to deal with that... I hope you don't mind. I am also adding a changelog entry crediting the bug fix to you, since you provided the original bug fix.