Add more asserts and ToStrings around the FakeProperty.Setter problem

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -3340,6 +3340,7 @@ namespace ICSharpCode.Decompiler.CSharp
 						{
 							var property = (IProperty)lastElement.Member;
 							Debug.Assert(property.IsIndexer);
+							Debug.Assert(property.Setter != null, $"Indexer property {property} has no setter");
 							elementsStack.Peek().Add(
 								new CallBuilder(this, typeSystem, settings)
 									.BuildDictionaryInitializerExpression(lastElement.OpCode, property.Setter, initObjRR, GetIndices(lastElement.Indices, indexVariables).ToList(), info.Values.Single())

ICSharpCode.Decompiler/TypeSystem/Implementation/FakeMember.cs

@@ -199,6 +199,16 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 		public bool IsIndexer { get; set; }
 		public bool ReturnTypeIsRefReadOnly => false;
 		public IReadOnlyList<IParameter> Parameters { get; set; }
+
+		public override string ToString() =>
+			"FakeProperty " + ReturnType + " " + DeclaringType.Name + "." + Name +
+				(Parameters.Count == 0
+					? ""
+					: "[" + string.Join(", ", Parameters) + "]") +
+				" { " +
+					(CanGet ? "get; " : "") +
+					(CanSet ? "set; " : "") +
+				"}";
 	}
 
 	sealed class FakeEvent : FakeMember, IEvent