Add missing KeyType documentation

src/Microsoft.ML.Core/Data/KeyType.cs

@@ -59,6 +59,13 @@ public static bool IsValidDataType(Type type)
         /// </summary>
         public ulong Count { get; }
 
+        /// <summary>
+        /// Determine if this <see cref="KeyType"/> object is equal to another <see cref="DataViewType"/> instance.
+        /// Checks if the other item is the type of <see cref="KeyType"/>, if the RawType
+        /// is the same, and if the Count is the same.
+        /// </summary>
+        /// <param name="other">The other object to compare against.</param>
+        /// <returns><see langword="true" /> if both objects are equal, otherwise <see langword="false"/>.</returns>
         public override bool Equals(DataViewType other)
         {
             if (other == this)
@@ -73,16 +80,31 @@ public override bool Equals(DataViewType other)
             return true;
         }
 
+        /// <summary>
+        /// Determine if a <see cref="KeyType"/> instance is equal to another <see cref="KeyType"/> instance.
+        /// Checks if any object is the type of <see cref="KeyType"/>, if the RawType
+        /// is the same, and if the Count is the same.
+        /// </summary>
+        /// <param name="other">The other object to compare against.</param>
+        /// <returns><see langword="true" /> if both objects are equal, otherwise <see langword="false"/>.</returns>
         public override bool Equals(object other)
         {
             return other is DataViewType tmp && Equals(tmp);
         }
 
+        /// <summary>
+        /// Retrieves the hash code.
+        /// </summary>
+        /// <returns>An integer representing the hash code.</returns>
         public override int GetHashCode()
         {
             return Hashing.CombinedHash(RawType.GetHashCode(), Count);
         }
 
+        /// <summary>
+        /// The string representation of the <see cref="KeyType"/>.
+        /// </summary>
+        /// <returns>A formatted string.</returns>
         public override string ToString()
         {
             InternalDataKind rawKind = this.GetRawKind();