Add table and view metadata messges (#296)

* Add SMO table property lookup event

* Fix a couple bugs in column metadata

* Add GetView metadata message

src/Microsoft.SqlTools.ServiceLayer/Metadata/Contracts/TableMetadata.cs

@@ -0,0 +1,85 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Linq;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
+using Microsoft.SqlTools.Utility;
+
+namespace Microsoft.SqlTools.ServiceLayer.Metadata
+{
+    /// <summary>
+    /// Provides metadata about the table or view being edited
+    /// </summary>
+    public class TableMetadata
+    {
+        /// <summary>
+        /// Constructs a simple edit table metadata provider
+        /// </summary>
+        public TableMetadata()
+        {
+            HasExtendedProperties = false;
+        }
+
+        #region Basic Properties (properties provided by SMO)
+
+        /// <summary>
+        /// List of columns in the object being edited
+        /// </summary>
+        public ColumnMetadata[] Columns { get; set; }
+
+        /// <summary>
+        /// Full escaped multipart identifier for the object being edited
+        /// </summary>
+        public string EscapedMultipartName { get; set; }
+
+        /// <summary>
+        /// Whether or not the object being edited is memory optimized
+        /// </summary>
+        public bool IsMemoryOptimized { get; set; }
+
+        #endregion
+
+        #region Extended Properties (properties provided by SqlClient)
+
+        /// <summary>
+        /// Whether or not the table has had extended properties added to it
+        /// </summary>
+        public bool HasExtendedProperties { get; private set; }
+
+        /// <summary>
+        /// List of columns that are used to uniquely identify a row
+        /// </summary>
+        public ColumnMetadata[] KeyColumns { get; private set; }
+
+        #endregion
+
+        /// <summary>
+        /// Extracts extended column properties from the database columns from SQL Client
+        /// </summary>
+        /// <param name="dbColumnWrappers">The column information provided by SQL Client</param>
+        public void Extend(DbColumnWrapper[] dbColumnWrappers)
+        {
+            Validate.IsNotNull(nameof(dbColumnWrappers), dbColumnWrappers);
+
+            // Iterate over the column wrappers and improve the columns we have
+            for (int i = 0; i < Columns.Length; i++)
+            {
+                Columns[i].Extend(dbColumnWrappers[i]);
+            }
+
+            // Determine what the key columns are
+            KeyColumns = Columns.Where(c => c.IsKey.HasTrue()).ToArray();
+            if (KeyColumns.Length == 0)
+            {
+                // We didn't find any explicit key columns. Instead, we'll use all columns that are
+                // trustworthy for uniqueness (usually all the columns)
+                KeyColumns = Columns.Where(c => c.IsTrustworthyForUniqueness.HasTrue()).ToArray();
+            }
+
+            // Mark that the table is now extended
+            HasExtendedProperties = true;
+        }
+    }
+}