Make PEvents and PTypes serializable in java (#726)

Author: mchadalavada

Src/PCompiler/CompilerCore/Backend/Java/EventGenerator.cs

@@ -51,7 +51,7 @@ private void WriteEventDecl(PEvent e)
             var payloadType = argType.TypeName;
             var payloadRefType = argType.ReferenceTypeName;
 
-            WriteLine($"public static class {eventName} extends {Constants.PEventsClass}<{payloadRefType}> {{");
+            WriteLine($"public static class {eventName} extends {Constants.PEventsClass}<{payloadRefType}> implements Serializable {{");
 
             var hasPayload = !(argType is TypeManager.JType.JVoid);
             if (hasPayload)

Src/PCompiler/CompilerCore/Backend/Java/TypesGenerator.cs

@@ -109,7 +109,7 @@ private void WriteNamedTupleDecl(NamedTupleType t)
             }
 
             var tname = Names.NameForNamedTuple(t);
-            WriteLine($"public static class {tname} implements {Constants.PValueClass}<{tname}> {{");
+            WriteLine($"public static class {tname} implements {Constants.PValueClass}<{tname}>, Serializable {{");
             WriteLine($"// {t.CanonicalRepresentation}");
 
             WriteNamedTupleFields(fields);