Porting showplan code from ssms (#1280)

* Porting showplan code from ssms

* Moving showplans bits to a subfolder

* code cleanup

* Remvoing unnecssary conditional visibility

src/Microsoft.SqlTools.ServiceLayer/ShowPlan/ShowPlanGraph/IXmlBatchParser.cs

@@ -0,0 +1,31 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+namespace Microsoft.SqlTools.ServiceLayer.ShowPlan.ShowPlanGraph
+{
+    /// <summary>
+    /// Interface represents ability to split an data source containing multiple
+    /// batches / statement into statements and return an XML containing a single statement.
+    /// This is used for XML ShowPlan saving.
+    /// </summary>
+    public interface IXmlBatchParser
+	{
+        /// <summary>
+        /// Builds one or more Graphs that
+        /// represnet data from the data source.
+        /// </summary>
+        /// <param name="dataSource">Data Source.</param>
+        /// <returns>An array of AnalysisServices Graph objects.</returns>
+		string GetSingleStatementXml(object dataSource, int statementIndex);
+
+        /// <summary>
+        /// Returns statements block type object
+        /// </summary>
+        /// <param name="dataSource">Data source</param>
+        /// <param name="statementIndex">Statement index in the data source</param>
+        /// <returns>Statement block type object</returns>
+        StmtBlockType GetSingleStatementObject(object dataSource, int statementIndex);
+	}
+}