Remove Delegate.Method use in EventRegistrationTokenTable<T>

[Sergio0694]

Overview

NativeAOT in .NET 9 is getting better trimming when using delegates (specifically, allowing delegate targets to not be considered reflection visible, see dotnet/runtime#96166). But, this is currently completely blocked because we're accessing Delegate.Method in our EventRegistrationTokenTable<T> type, which completely disables this optimization (as it could otherwise break):

CsWinRT/src/cswinrt/strings/WinRT.cs

Lines 1132 to 1144 in ae69551

	uint handlerHashCode;
	global::System.Delegate[] invocationList = ((global::System.Delegate)(object)handler).GetInvocationList();
	if (invocationList.Length == 1)
	{
	handlerHashCode = (uint)invocationList[0].Method.GetHashCode();
	}
	else
	{
	handlerHashCode = (uint)handler.GetHashCode();
	}
	ulong tokenValue = ((ulong)(uint)typeof(T).GetHashCode() << 32) | handlerHashCode;
	return new EventRegistrationToken { Value = (long)tokenValue };

We need to drop that Delegate.Method use to allow saving a fair amount of binary size with NativeAOT builds.
With a minimal WinRT component, doing so saves over 200 KB:

See: dotnet/runtime#96947.