Environment variables helper (#2673)

Issue https://github.com/microsoft/Power-Fx/issues/2416.

src/libraries/Microsoft.PowerFx.Core/Public/Values/CompileTimeTypeWrapperRecordValue.cs

@@ -43,11 +43,11 @@ namespace Microsoft.PowerFx.Types
 
         protected override bool TryGetField(FormulaType fieldType, string fieldName, out FormulaValue result)
         {
-            if (Type.TryGetFieldType(fieldName, out var compileTimeType))
+            if (Type.TryGetFieldType(fieldName, out var logical, out var compileTimeType))
             {
                 // Only return field which were specified via the expectedType (IE RecordType),
                 // because inner record value may have more fields than the expected type.
-                if (compileTimeType == fieldType && _fields.TryGetValue(fieldName, out result))
+                if (compileTimeType == fieldType && _fields.TryGetValue(logical, out result))
                 {
                     return true;
                 }

src/libraries/Microsoft.PowerFx.Interpreter/Environment/PowerFxConfigExtensions.cs

@@ -7,6 +7,7 @@ using Microsoft.PowerFx.Core.Functions;
 using Microsoft.PowerFx.Core.Texl.Builtins;
 using Microsoft.PowerFx.Functions;
 using Microsoft.PowerFx.Interpreter;
+using Microsoft.PowerFx.Types;
 
 namespace Microsoft.PowerFx
 {
@@ -22,6 +23,12 @@ namespace Microsoft.PowerFx
             symbolTable.AddFunction(function.GetTexlFunction());
         }
 
+        public static void AddEnvironmentVariables(this SymbolValues symbolValues, RecordValue recordValue)
+        {
+            var variablesRecordValue = FormulaValue.NewRecordFromFields(new NamedValue("Variables", recordValue));
+            symbolValues.Add("Environment", variablesRecordValue);
+        }
+
         /// <summary>
         /// Enable a Set() function which allows scripts to do <see cref="RecalcEngine.UpdateVariable(string, Types.FormulaValue, SymbolProperties)"/>.
         /// </summary>

src/tests/Microsoft.PowerFx.Core.Tests.Shared/Helpers/TestTabularDataSource.cs

@@ -124,7 +124,7 @@ namespace Microsoft.PowerFx.Core.Tests.Helpers
 
         public DType Schema => throw new NotImplementedException();
 
-        public BidirectionalDictionary<string, string> DisplayNameMapping => throw new NotImplementedException();
+        public BidirectionalDictionary<string, string> DisplayNameMapping => new BidirectionalDictionary<string, string>();
 
         public BidirectionalDictionary<string, string> PreviousDisplayNameMapping => throw new NotImplementedException();