Add a helper method for getting a dialog

Right now a couple of methods use `DialogHelpers.FindDialog` to try to locate an open dialog, and then throw an `InvalidOperationException` if they don't find it. This is going to be a pretty common pattern when working with dialogs and controls within dialogs, so I've refactored it into a new `DialogHelpers.GetOpenDialog` method.

I've also updated the `Editor_InProc.PressDialogButton` method to make use of the `AutomationElement` extension methods.

src/VisualStudio/IntegrationTest/TestUtilities/InProcess/DialogHelpers.cs

-using System;
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -11,6 +13,23 @@ namespace Microsoft.VisualStudio.IntegrationTest.Utilities.InProcess
 {
     public static class DialogHelpers
     {
+        /// <summary>
+        /// Returns an <see cref="AutomationElement"/> representing the open dialog with automation ID
+        /// <paramref name="dialogAutomationName"/>.
+        /// Throws an <see cref="InvalidOperationException"/> if an open dialog with that name cannot be
+        /// found.
+        /// </summary>
+        public static AutomationElement GetOpenDialog(int visualStudioHWnd, string dialogAutomationName)
+        {
+            var dialogAutomationElement = FindDialog(visualStudioHWnd, dialogAutomationName, isOpen: true);
+            if (dialogAutomationElement == null)
+            {
+                throw new InvalidOperationException($"Expected the {dialogAutomationName} dialog to be open, but it is not.");
+            }
+
+            return dialogAutomationElement;
+        }
+
         public static AutomationElement FindDialog(int visualStudioHWnd, string dialogAutomationName, bool isOpen)
         {
             return Retry(

src/VisualStudio/IntegrationTest/TestUtilities/InProcess/Editor_InProc.cs

@@ -122,6 +122,8 @@ public string GetLineTextBeforeCaret()
                 return text.Substring(0, bufferPosition.Position - line.Start);
             });
 
+
+
         public string GetLineTextAfterCaret()
             => ExecuteOnActiveView(view =>
             {
@@ -420,11 +422,7 @@ public void VerifyDialog(string dialogAutomationId, bool isOpen)
 
         public void DialogSendKeys(string dialogAutomationName, string keys)
         {
-            var dialogAutomationElement = DialogHelpers.FindDialog(GetDTE().MainWindow.HWnd, dialogAutomationName, isOpen: true);
-            if (dialogAutomationElement == null)
-            {
-                throw new InvalidOperationException($"Expected the {dialogAutomationName} dialog to be open, but it is not.");
-            }
+            var dialogAutomationElement = DialogHelpers.GetOpenDialog(GetDTE().MainWindow.HWnd, dialogAutomationName);
 
             dialogAutomationElement.SetFocus();
             SendKeys.SendWait(keys);
@@ -432,29 +430,10 @@ public void DialogSendKeys(string dialogAutomationName, string keys)
 
         public void PressDialogButton(string dialogAutomationName, string buttonAutomationName)
         {
-            var dialogAutomationElement = DialogHelpers.FindDialog(GetDTE().MainWindow.HWnd, dialogAutomationName, isOpen: true);
-            if (dialogAutomationElement == null)
-            {
-                throw new InvalidOperationException($"Expected the {dialogAutomationName} dialog to be open, but it is not.");
-            }
-
-            Condition condition = new PropertyCondition(AutomationElement.AutomationIdProperty, buttonAutomationName);
-
-            var buttonAutomationElement = dialogAutomationElement.FindFirst(TreeScope.Descendants, condition);
+            var dialogAutomationElement = DialogHelpers.GetOpenDialog(GetDTE().MainWindow.HWnd, dialogAutomationName);
 
-            if (buttonAutomationElement == null)
-            {
-                throw new InvalidOperationException($"Could not find the {buttonAutomationName} button in the {dialogAutomationName} dialog");
-            }
-
-            if (buttonAutomationElement.TryGetCurrentPattern(InvokePattern.Pattern, out var invokePattern))
-            {
-                (invokePattern as InvokePattern).Invoke();
-            }
-            else
-            {
-                throw new InvalidOperationException($"The element {buttonAutomationName} does not have an InvokePattern. Please make sure that it is the correct control");
-            }
+            var buttonAutomationElement = dialogAutomationElement.FindDescendantByAutomationId(buttonAutomationName);
+            buttonAutomationElement.Invoke();
         }
     }
 }