Fix null checks on UnityEngine.Object types

- Unity has special handling for checking if a UnityEngine.Object is null or not that has unexpected different behavior from how System.Object compares things. This was causing issues to always use System.Object equality on all null checks since some Unity functions return a non-null object that is still considered "null" by unity.

Assets/UdonSharp/Editor/UdonSharpASTVisitor.cs

@@ -1114,7 +1114,13 @@ private MethodInfo[] GetOperators(System.Type type, BuiltinOperatorType builtinO
 
             operatorName = $"op_{operatorName}";
 
-            foundOperators.AddRange(type.GetMethods(BindingFlags.Public | BindingFlags.Static).Where(e => e.Name == operatorName));
+            System.Type currentType = type;
+
+            while (currentType != null)
+            {
+                foundOperators.AddRange(currentType.GetMethods(BindingFlags.Public | BindingFlags.Static).Where(e => e.Name == operatorName));
+                currentType = currentType.BaseType;
+            }
 
             // Add the object equality and inequality operators if we haven't already found better matches
             if (foundOperators.Count == 0 && type != typeof(object) && !type.IsValueType &&
@@ -1446,6 +1452,25 @@ public override void VisitBinaryExpression(BinaryExpressionSyntax node)
 
                     SymbolDefinition resultSymbol = null;
 
+                    BuiltinOperatorType operatorType = SyntaxKindToBuiltinOperator(node.Kind());
+
+                    // Basic handling for handling null equality/inequality on derived types since Unity has special behavior for comparing UnityEngine.Object types to null
+                    if (operatorType == BuiltinOperatorType.Equality ||
+                        operatorType == BuiltinOperatorType.Inequality)
+                    {
+                        bool lhsNull = lhsValue.declarationType.HasFlag(SymbolDeclTypeFlags.Constant) && lhsValue.symbolDefaultValue == null;
+                        bool rhsNull = rhsValue.declarationType.HasFlag(SymbolDeclTypeFlags.Constant) && rhsValue.symbolDefaultValue == null;
+
+                        if (lhsNull && !rhsNull)
+                        {
+                            lhsValue = visitorContext.topTable.CreateConstSymbol(rhsType, null);
+                        }
+                        else if (rhsNull && !lhsNull)
+                        {
+                            rhsValue = visitorContext.topTable.CreateConstSymbol(lhsType, null);
+                        }
+                    }
+
                     try
                     {
                         resultSymbol = operatorMethodCapture.Invoke(new SymbolDefinition[] { lhsValue, rhsValue });