Make filtered indexes actually work

Fixes #286

src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs

@@ -562,6 +562,13 @@ protected override void Generate(RenameTableOperation operation, [CanBeNull] IMo
                 .Append(ColumnList(operation.Columns))
                 .Append(")");
 
+            if (!string.IsNullOrEmpty(operation.Filter))
+            {
+                builder
+                    .Append(" WHERE ")
+                    .Append(operation.Filter);
+            }
+
             builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
 
             EndStatement(builder);