Adds Count Capabilites.

Author: jas-valgotar

src/libraries/Microsoft.PowerFx.Connectors/Public/CdpTableValue.cs

@@ -66,6 +66,11 @@ public void Refresh()
         {
             _cachedRows = null;
         }
+
+        public Task<int> GetCountAsync(IServiceProvider services, DelegationParameters parameters, CancellationToken cancel)
+        {
+            throw new NotImplementedException();
+        }
     }   
 
     internal static class ODataParametersExtensions

src/libraries/Microsoft.PowerFx.Core/Entities/External/TableDelegationInfo.cs

@@ -26,6 +26,9 @@ public abstract class TableDelegationInfo
         [Obsolete("preview")]
         public SummarizeCapabilities SummarizeCapabilities { get; init; }
 
+        [Obsolete("preview")]
+        public CountCapabilities CountCapabilities { get; init; }
+
         // Defines ungroupable columns
         public GroupRestrictions GroupRestriction { get; init; }
 
@@ -299,6 +302,29 @@ public enum SummarizeMethod
         CountRows
     }
 
+    [Obsolete("preview")]
+    public class CountCapabilities
+    {
+        public CountCapabilities()
+        {
+        }
+
+        public virtual bool IsCountableTable()
+        {
+            return false;
+        }
+
+        public virtual bool IsCountableAfterJoin()
+        {
+            return false;
+        }
+
+        public virtual bool IsCountableAfterSummarize()
+        {
+            return false;
+        }
+    }
+
     public sealed class FilterRestrictions
     {
         // List of required properties

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

@@ -28,6 +28,15 @@ public interface IDelegatableTableValue
         /// <param name="cancel"></param>
         /// <returns></returns>
         Task<IReadOnlyCollection<DValue<RecordValue>>> GetRowsAsync(IServiceProvider services, DelegationParameters parameters, CancellationToken cancel);
+
+        /// <summary>
+        /// Evaluation will invoke this method on delegated count calls.
+        /// </summary>
+        /// <param name="services">Pre-eval services.</param>
+        /// <param name="parameters">Delegation parameters.</param>
+        /// <param name="cancel"></param>
+        /// <returns>Return total count of rows. Returns -1 if rows could not be counted.</returns>
+        Task<int> GetCountAsync(IServiceProvider services, DelegationParameters parameters, CancellationToken cancel);
     }
 
     /// <summary>