CollectNamespacesForDecompilation:

- support for marshal info
 - support for secdecls
 - add base types of referenced types as well, to cover all possible casts that are implicit in IL, but need to be explicit in C#.

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -450,6 +450,14 @@ namespace ICSharpCode.Decompiler.CSharp
 					} else {
 						namespaces.Add(typeRef.Namespace);
 					}
+					if (visited.Add(typeRef)) {
+						var typeDef = typeRef.Resolve();
+						if (typeDef != null) {
+							CollectNamespacesForDecompilation(typeDef.BaseType, namespaces, visited);
+							foreach (var intf in typeDef.Interfaces)
+								CollectNamespacesForDecompilation(intf.InterfaceType, namespaces, visited);
+						}
+					}
 					break;
 				case FieldReference fieldRef:
 					CollectNamespacesForDecompilation(fieldRef.DeclaringType, namespaces, visited);
@@ -539,8 +547,12 @@ namespace ICSharpCode.Decompiler.CSharp
 					CollectAttributes(cap);
 				}
 				if (def is ISecurityDeclarationProvider sdp) {
+					namespaces.Add("System.Security.Permissions");
 					CollectSecurityDeclarations(sdp);
 				}
+				if (def is IMarshalInfoProvider mip && mip.HasMarshalInfo) {
+					namespaces.Add("System.Runtime.InteropServices");
+				}
 				switch (def) {
 					case TypeDefinition typeDef:
 						if (typeDef.IsNested) {