Use Dictionary with StringComparer to avoid string allocations in System.Data.Common (#120603)

Author: Alex-Sob

src/libraries/System.Data.Common/src/System/Data/Common/AdapterUtil.Common.cs

@@ -779,15 +779,14 @@ internal static DataRow[] SelectAdapterRows(DataTable dataTable, bool sorted)
         // { "a", "A", "a1" } -> { "a", "A2", "a1" }
         internal static void BuildSchemaTableInfoTableNames(string[] columnNameArray)
         {
-            Dictionary<string, int> hash = new Dictionary<string, int>(columnNameArray.Length);
+            Dictionary<string, int> hash = new Dictionary<string, int>(columnNameArray.Length, StringComparer.InvariantCultureIgnoreCase);
 
             int startIndex = columnNameArray.Length; // lowest non-unique index
             for (int i = columnNameArray.Length - 1; 0 <= i; --i)
             {
                 string columnName = columnNameArray[i];
                 if ((null != columnName) && (0 < columnName.Length))
                 {
-                    columnName = columnName.ToLowerInvariant();
                     int index;
                     if (hash.TryGetValue(columnName, out index))
                     {
@@ -813,7 +812,6 @@ internal static void BuildSchemaTableInfoTableNames(string[] columnNameArray)
                 }
                 else
                 {
-                    columnName = columnName.ToLowerInvariant();
                     if (i != hash[columnName])
                     {
                         GenerateUniqueName(hash, ref columnNameArray[i], i, 1);
@@ -827,8 +825,7 @@ private static int GenerateUniqueName(Dictionary<string, int> hash, ref string c
             for (; ; ++uniqueIndex)
             {
                 string uniqueName = columnName + uniqueIndex.ToString(CultureInfo.InvariantCulture);
-                string lowerName = uniqueName.ToLowerInvariant();
-                if (hash.TryAdd(lowerName, index))
+                if (hash.TryAdd(uniqueName, index))
                 {
                     columnName = uniqueName;
                     break;