Export to Markdown Support (#1705)

* Adding file writer for Markdown tables. No testing yet.

* Unit tests for the markdown writer

* Wiring up the factory and and request types

* Wiring up changes for Markdown serialization in serialization service

* Couple last minute tweaks

* Changes as per PR comments

* Revert temp testing code. 🙈

* Fluent assertions in SerializationServiceTests.cs

Co-authored-by: Ben Russell <russellben@microsoft.com>

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/Contracts/SaveResultsRequest.cs

@@ -84,7 +84,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
         public string Delimiter { get; set; }
 
         /// <summary>
-        /// either CR, CRLF or LF to seperate rows in CSV
+        /// either CR, CRLF or LF to separate rows in CSV
         /// </summary>
         public string LineSeperator { get; set; }
 
@@ -123,6 +123,28 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
         //TODO: define config for save as JSON
     }
 
+    /// <summary>
+    /// Parameters for saving results as a Markdown table
+    /// </summary>
+    public class SaveResultsAsMarkdownRequestParams : SaveResultsRequestParams
+    {
+        /// <summary>
+        /// Encoding of the CSV file
+        /// </summary>
+        public string Encoding { get; set; }
+
+        /// <summary>
+        /// Whether to include column names as header for the table.
+        /// </summary>
+        public bool IncludeHeaders { get; set; }
+
+        /// <summary>
+        /// Character sequence to separate a each row in the table. Should be either CR, CRLF, or
+        /// LF. If not provided, defaults to the system default line ending sequence.
+        /// </summary>
+        public string? LineSeparator { get; set; }
+    }
+
     /// <summary>
     /// Parameters to save results as XML
     /// </summary>
@@ -179,6 +201,16 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
             RequestType<SaveResultsAsJsonRequestParams, SaveResultRequestResult> Type =
             RequestType<SaveResultsAsJsonRequestParams, SaveResultRequestResult>.Create("query/saveJson");
     }
+
+    /// <summary>
+    /// Request type to save results as a Markdown table
+    /// </summary>
+    public class SaveResultsAsMarkdownRequest
+    {
+        public static readonly
+            RequestType<SaveResultsAsMarkdownRequestParams, SaveResultRequestResult> Type =
+            RequestType<SaveResultsAsMarkdownRequestParams, SaveResultRequestResult>.Create("query/saveMarkdown");
+    }
     
     /// <summary>
     /// Request type to save results as XML