Fix issue where native apps throw errors when session transcription enabled

Resolves #396
Resolves PowerShell/vscode-powershell#972

Author: daviwil

src/PowerShellEditorServices/Session/Host/SimplePSHostRawUserInterface.cs

@@ -176,11 +176,7 @@ public override void FlushInputBuffer()
         /// <returns>A BufferCell array with the requested buffer contents.</returns>
         public override BufferCell[,] GetBufferContents(Rectangle rectangle)
         {
-            Logger.Write(
-                LogLevel.Warning,
-                "PSHostRawUserInterface.GetBufferContents was called");
-
-            throw new System.NotImplementedException();
+            return new BufferCell[0,0];
         }
 
         /// <summary>

src/PowerShellEditorServices/Session/Host/TerminalPSHostRawUserInterface.cs

@@ -208,11 +208,7 @@ public override void FlushInputBuffer()
         /// <returns>A BufferCell array with the requested buffer contents.</returns>
         public override BufferCell[,] GetBufferContents(Rectangle rectangle)
         {
-            Logger.Write(
-                LogLevel.Warning,
-                "PSHostRawUserInterface.GetBufferContents was called");
-
-            throw new System.NotImplementedException();
+            return new BufferCell[0,0];
         }
 
         /// <summary>