Disregard parameter names in ExpressionEqualityComparer.GetHashCode

The `GetHashCode` now bases the hash code of each parameter expression
on its position in the containing lambda(s) parameter list, thereby
making it so that otherwise identical lambda expressions whose only
difference is the parameter names to yield the same hash code.

Fixes dotnet#30697

src/EFCore/Query/ExpressionEqualityComparer.cs

@@ -30,6 +30,8 @@ private ExpressionEqualityComparer()
     /// </summary>
     public static ExpressionEqualityComparer Instance { get; } = new();
 
+    private List<ParameterExpression>? _lambdaParameters;
+
     /// <inheritdoc />
     public int GetHashCode(Expression obj)
     {
@@ -110,9 +112,21 @@ public int GetHashCode(Expression obj)
                     break;
 
                 case LambdaExpression lambdaExpression:
+                    _lambdaParameters ??= new();
+                    foreach (var p in lambdaExpression.Parameters)
+                    {
+                        _lambdaParameters.Add(p);
+                    }
+
                     hash.Add(lambdaExpression.Body, this);
                     AddListToHash(lambdaExpression.Parameters);
                     hash.Add(lambdaExpression.ReturnType);
+
+                    foreach (var p in lambdaExpression.Parameters)
+                    {
+                        _lambdaParameters.Remove(p);
+                    }
+
                     break;
 
                 case ListInitExpression listInitExpression:
@@ -161,7 +175,15 @@ public int GetHashCode(Expression obj)
                     break;
 
                 case ParameterExpression parameterExpression:
-                    AddToHashIfNotNull(parameterExpression.Name);
+                    int? index = _lambdaParameters?.IndexOf(parameterExpression);
+                    if (index > -1)
+                    {
+                        hash.Add(index);
+                    }
+                    else
+                    {
+                        AddToHashIfNotNull(parameterExpression.Name);
+                    }
                     break;
 
                 case RuntimeVariablesExpression runtimeVariablesExpression: