Enable PDF files in preview pane (#9088)

## Summary of the Pull Request
This PR enables user to preview PDF files in the Explorer preview pane
and in Outlook. 

**What is this about:**
Windows does not support out of the box experience for previewing PDF
files in the preview pane. Users need to install third-party software
like Adobe Acrobat reader. The PdfPreviewHandler module enbales the user
to preview PDF files.

**How does someone test / validate:** 
Run the installer, open Explorer and select a PDF file, enable the
preview pane. Maybe need to remove third-party PDF software.

## Quality Checklist

- [X] **Linked issue:** #3548
- [ ] **Communication:** I've discussed this with core contributors in the issue. 
- [X] **Tests:** Added/updated and all pass
- [X] **Installer:** Added/updated and all pass
- [X] **Localization:** All end user facing strings can be localized
- [ ] **Docs:** Added/ updated
- [x] **Binaries:** Any new files are added to WXS / YML
   - [ ] No new binaries
   - [x] YML for signing
   - [x] WXS for installer

src/modules/previewpane/UnitTests-PdfPreviewHandler/PdfPreviewHandlerTest.cs

@@ -0,0 +1,89 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Drawing;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Runtime.InteropServices.ComTypes;
+using System.Windows.Forms;
+using Microsoft.PowerToys.PreviewHandler.Pdf;
+using Microsoft.PowerToys.STATestExtension;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Moq;
+
+namespace PdfPreviewHandlerUnitTests
+{
+    [STATestClass]
+    public class PdfPreviewHandlerTest
+    {
+        [TestMethod]
+        public void PdfPreviewHandlerControlAddsControlsToFormWhenDoPreviewIsCalled()
+        {
+            // Arrange
+            using (var pdfPreviewHandlerControl = new PdfPreviewHandlerControl())
+            {
+                // Act
+                var file = File.ReadAllBytes("HelperFiles/sample.pdf");
+
+                pdfPreviewHandlerControl.DoPreview<IStream>(GetMockStream(file));
+
+                var flowLayoutPanel = pdfPreviewHandlerControl.Controls[0] as FlowLayoutPanel;
+
+                // Assert
+                Assert.AreEqual(1, pdfPreviewHandlerControl.Controls.Count);
+            }
+        }
+
+        [TestMethod]
+        public void PdfPreviewHandlerControlShouldAddValidInfoBarIfPdfPreviewThrows()
+        {
+            // Arrange
+            using (var pdfPreviewHandlerControl = new PdfPreviewHandlerControl())
+            {
+                var mockStream = new Mock<IStream>();
+                mockStream
+                    .Setup(x => x.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<IntPtr>()))
+                    .Throws(new Exception());
+
+                // Act
+                pdfPreviewHandlerControl.DoPreview(mockStream.Object);
+                var textBox = pdfPreviewHandlerControl.Controls[0] as RichTextBox;
+
+                // Assert
+                Assert.IsFalse(string.IsNullOrWhiteSpace(textBox.Text));
+                Assert.AreEqual(1, pdfPreviewHandlerControl.Controls.Count);
+                Assert.AreEqual(DockStyle.Top, textBox.Dock);
+                Assert.AreEqual(Color.LightYellow, textBox.BackColor);
+                Assert.IsTrue(textBox.Multiline);
+                Assert.IsTrue(textBox.ReadOnly);
+                Assert.AreEqual(RichTextBoxScrollBars.None, textBox.ScrollBars);
+                Assert.AreEqual(BorderStyle.None, textBox.BorderStyle);
+            }
+        }
+
+        private static IStream GetMockStream(byte[] sourceArray)
+        {
+            var streamMock = new Mock<IStream>();
+            var firstCall = true;
+            streamMock
+                .Setup(x => x.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<IntPtr>()))
+                .Callback<byte[], int, IntPtr>((buffer, countToRead, bytesReadPtr) =>
+                {
+                    if (firstCall)
+                    {
+                        Array.Copy(sourceArray, 0, buffer, 0, sourceArray.Length);
+                        Marshal.WriteInt32(bytesReadPtr, sourceArray.Length);
+                        firstCall = false;
+                    }
+                    else
+                    {
+                        Marshal.WriteInt32(bytesReadPtr, 0);
+                    }
+                });
+
+            return streamMock.Object;
+        }
+    }
+}