Fix column mapping in GroupBy and aggregation queries to ensure corre… (#3750)

## Why make this change?
There is a bug when running aggregation queries, wherein if a mapping
backed column is present, the aggregation fails since it references the
surfaced column and not the backed column.

This pull request improves how group-by queries with mapped (aliased)
columns are handled in SQL generation and adds a regression test to
ensure correct behavior. The main focus is to ensure that SQL queries
reference the backing (database) column names in the SELECT and GROUP BY
clauses, while projecting the correct exposed (mapped) names in the
results.



## What is this change?

* Updated `ProcessGroupByField` and `ProcessGroupByFieldSelections` in
`SqlQueryStructure.cs` to ensure that the backing (database) column name
is used in the SQL query, while the exposed (mapped) field name is used
as the label in the results. This resolves previous issues where the
SELECT clause referenced the exposed name instead of the actual database
column.
[[1]](diffhunk://#diff-4b3df270873038f36ec2f627091120b7aafa271c0e2a2d257380f90602f5a298L907-R908)
[[2]](diffhunk://#diff-4b3df270873038f36ec2f627091120b7aafa271c0e2a2d257380f90602f5a298L956-R956)

## How was this tested?

- [x] Integration Tests
- [X] Unit Tests

* Added a new test method
`TestSupportForGroupByAggregationWithMappedColumns` in
`MsSqlGraphQLQueryTests.cs` to verify that group-by fields and
aggregations both resolve to the correct backing columns, and that
results are projected under the mapped names. This prevents regressions
on mapped column handling in group-by queries.
* Added missing import for
`Azure.DataApiBuilder.Service.GraphQLBuilder.Queries` in
`MsSqlGraphQLQueryTests.cs` to support the new test.

---------

Co-authored-by: ARPIT GUPTA <guptaar@microsoft.com>

Author: ar-guptaar

src/Core/Resolvers/Sql Query Structures/SqlQueryStructure.cs

@@ -905,7 +905,7 @@ private void ProcessGroupByField(FieldNode groupByField, IMiddlewareContext ctx,
                     }
 
                     GroupByMetadata.Fields[columnName] = new Column(DatabaseObject.SchemaName, DatabaseObject.Name, columnName, SourceAlias);
-                    AddColumn(fieldName, backingColumn ?? fieldName);
+                    AddColumn(columnName: columnName, labelName: fieldName);
                     fieldsInArgument.Add(fieldName);
                 }
             }
@@ -953,7 +953,7 @@ private void ProcessGroupByFieldSelections(FieldNode groupByFieldSelection, Hash
                 }
 
                 string columnName = MetadataProvider.TryGetBackingColumn(EntityName, fieldName, out string? backingColumn) ? backingColumn : fieldName;
-                AddColumn(fieldName, columnName);
+                AddColumn(columnName: columnName, labelName: fieldName);
             }
 
         }

src/Core/Resolvers/SqlPaginationUtil.cs

@@ -54,6 +54,10 @@ public static JsonDocument CreatePaginationConnectionFromJsonDocument(JsonDocume
 
         private static string GenerateGroupByObjectFromResult(GroupByMetadata groupByMetadata, IEnumerable<JsonElement> rootEnumerated)
         {
+            HashSet<string> aggregationAliases = groupByMetadata.Aggregations
+                .Select(aggregation => aggregation.Column.OperationAlias)
+                .ToHashSet(StringComparer.Ordinal);
+
             JsonArray groupByArray = new();
             foreach (JsonElement element in rootEnumerated)
             {
@@ -62,16 +66,13 @@ private static string GenerateGroupByObjectFromResult(GroupByMetadata groupByMet
                 JsonObject combinedObject = new();
                 foreach (JsonProperty property in element.EnumerateObject())
                 {
-                    if (groupByMetadata.Fields.ContainsKey(property.Name))
+                    if (aggregationAliases.Contains(property.Name))
                     {
-                        if (groupByMetadata.RequestedFields)
-                        {
-                            fieldObject.Add(property.Name, JsonNode.Parse(property.Value.GetRawText()));
-                        }
+                        aggregationObject.Add(property.Name, JsonNode.Parse(property.Value.GetRawText()));
                     }
-                    else
+                    else if (groupByMetadata.RequestedFields)
                     {
-                        aggregationObject.Add(property.Name, JsonNode.Parse(property.Value.GetRawText()));
+                        fieldObject.Add(property.Name, JsonNode.Parse(property.Value.GetRawText()));
                     }
                 }