Edit Data Service (#241)

This is a very large change. I'll try to outline what's going on.

1. This adds the **EditDataService** which manages editing **Sessions**.
    1. Each session has a **ResultSet** (from the QueryExecutionService) which has the rows of the table and basic metadata about the columns 
    2. Each session also has an **IEditTableMetadata** implementation which is derived from SMO metadata which provides more in-depth and trustworthy data about the table than SqlClient alone can.
    3. Each session holds a list of **RowEditBase** abstract class implementations
        1. **RowUpdate** - Update cells in a row (generates `UPDATE` statement)
        2. **RowDelete** - Delete an entire row (generates `DELETE` statement)
        3. **RowCreate** - Add a new row (generates `INSERT INTO` statement)
    4. Row edits have a collection of **CellUpdates** that hold updates for individual cells (except for RowDelete)
        1. Cell updates are generated from text
     5. RowEditBase offers some baseline functionality
        1. Generation of `WHERE` clauses (which can be parameterized)
        2. Validation of whether a column can be updated
2. New API Actions
    1. edit/initialize - Queries for the contents of a table/view, builds SMO metadata, sets up a session
    2. edit/createRow - Adds a new RowCreate to the Session
    3. edit/deleteRow - Adds a new RowDelete to the Session
    4. edit/updateCell - Adds a CellUpdate to a RowCreate or RowUpdate in the Session
    5. edit/revertRow - Removes a RowCreate, RowDelete, or RowUpdate from the Session
    6. edit/script - Generates a script for the changes in the Session and stores to disk
    7. edit/dispose - Removes a Session and releases the query
3. Smaller updates (unit test mock improvements, tweaks to query execution service)

**There are more updates planned -- this is just to get eyeballs on the main body of code**

* Initial stubs for edit data service

* Stubbing out update management code

* Adding rudimentary dispose request

* More stubbing out of update row code

* Adding complete edit command contracts, stubbing out request handlers

* Adding basic implementation of get script

* More in progress work to implement base of row edits

* More in progress work to implement base of row edits

* Adding string => object conversion logic and various cleanup

* Adding a formatter for using values in scripts

* Splitting IMessageSender into IEventSender and IRequestSender

* Adding inter-service method for executing queries

* Adding inter-service method for disposing of a query

* Changing edit contract to include the object to edit

* Fully fleshing out edit session initialization

* Generation of delete scripts is working

* Adding scripter for update statements

* Adding scripting functionality for INSERT statements

* Insert, Update, and Delete all working with SMO metadata

* Polishing for SqlScriptFormatter

* Unit tests and reworked byte[] conversion

* Replacing the awful and inflexible Dictionary<string, string>[][] with a much better test data set class

* Fixing syntax error in generated UPDATE statements

* Adding unit tests for RowCreate

* Adding tests for the row edit base class

* Adding row delete tests

* Adding RowUpdate tests, validation for number of key columns

* Adding tests for the unit class

* Adding get script tests for the session

* Service integration tests, except initialization tests

* Service integration tests, except initialization tests

* Adding messages to sr.strings

* Adding messages to sr.strings

* Fixing broken unit tests

* Adding factory pattern for SMO metadata provider

* Copyright and other comments

* Addressing first round of comments

* Refactoring EditDataService to have a single method for handling
session-dependent operations
* Refactoring Edit Data contracts to inherit from a Session and Row
operation params base class
* Copyright additions
* Small tweak to strings
* Updated unit tests to test the refactors

* More revisions as per pull request comments

src/Microsoft.SqlTools.ServiceLayer/EditData/EditTableMetadata.cs

@@ -0,0 +1,99 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Diagnostics;
+using Microsoft.SqlServer.Management.Smo;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
+using Microsoft.SqlTools.ServiceLayer.Utility;
+
+namespace Microsoft.SqlTools.ServiceLayer.EditData
+{
+    /// <summary>
+    /// Provides metadata about the table or view being edited
+    /// </summary>
+    public class EditTableMetadata : IEditTableMetadata
+    {
+        private readonly List<EditColumnWrapper> columns;
+        private readonly List<EditColumnWrapper> keyColumns;
+
+        /// <summary>
+        /// Constructor that extracts useful metadata from the provided metadata objects
+        /// </summary>
+        /// <param name="dbColumns">DB columns from the ResultSet</param>
+        /// <param name="smoObject">SMO metadata object for the table/view being edited</param>
+        public EditTableMetadata(IList<DbColumnWrapper> dbColumns, TableViewTableTypeBase smoObject)
+        {
+            Validate.IsNotNull(nameof(dbColumns), dbColumns);
+            Validate.IsNotNull(nameof(smoObject), smoObject);
+
+            // Make sure that we have equal columns on both metadata providers
+            Debug.Assert(dbColumns.Count == smoObject.Columns.Count);
+
+            // Create the columns for edit usage
+            columns = new List<EditColumnWrapper>();
+            for (int i = 0; i < dbColumns.Count; i++)
+            {
+                Column smoColumn = smoObject.Columns[i];
+                DbColumnWrapper dbColumn = dbColumns[i];
+
+                // A column is trustworthy for uniqueness if it can be updated or it has an identity
+                // property. If both of these are false (eg, timestamp) we can't trust it to uniquely
+                // identify a row in the table
+                bool isTrustworthyForUniqueness = dbColumn.IsUpdatable || smoColumn.Identity;
+
+                EditColumnWrapper column = new EditColumnWrapper
+                {
+                    DbColumn = dbColumn,
+                    Ordinal = i,
+                    EscapedName = SqlScriptFormatter.FormatIdentifier(dbColumn.ColumnName),
+                    IsTrustworthyForUniqueness = isTrustworthyForUniqueness,
+
+                    // A key column is determined by whether it is in the primary key and trustworthy
+                    IsKey = smoColumn.InPrimaryKey && isTrustworthyForUniqueness
+                };
+                columns.Add(column);
+            }
+
+            // Determine what the key columns are
+            keyColumns = columns.Where(c => c.IsKey).ToList();
+            if (keyColumns.Count == 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).ToList();
+            }
+
+            // If a table is memory optimized it is Hekaton. If it's a view, then it can't be Hekaton
+            Table smoTable = smoObject as Table;
+            IsMemoryOptimized = smoTable != null && smoTable.IsMemoryOptimized;
+
+            // Escape the parts of the name
+            string[] objectNameParts = {smoObject.Schema, smoObject.Name};
+            EscapedMultipartName = SqlScriptFormatter.FormatMultipartIdentifier(objectNameParts);
+        }
+
+        /// <summary>
+        /// Read-only list of columns in the object being edited
+        /// </summary>
+        public IEnumerable<EditColumnWrapper> Columns => columns.AsReadOnly();
+
+        /// <summary>
+        /// Full escaped multipart identifier for the object being edited
+        /// </summary>
+        public string EscapedMultipartName { get; }
+
+        /// <summary>
+        /// Whether or not the object being edited is memory optimized
+        /// </summary>
+        public bool IsMemoryOptimized { get; }
+
+        /// <summary>
+        /// Read-only list of columns that are used to uniquely identify a row
+        /// </summary>
+        public IEnumerable<EditColumnWrapper> KeyColumns => keyColumns.AsReadOnly();
+    }
+}