Io abstraction (#7293)

Co-authored-by: p-storm <paul.de.man@gmail.com>

src/modules/previewpane/MarkdownPreviewHandler/HTMLParsingExtension.cs

@@ -2,8 +2,6 @@
 // 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.IO;
 using Markdig;
 using Markdig.Extensions.Figures;
 using Markdig.Extensions.Tables;

src/modules/previewpane/MarkdownPreviewHandler/MarkdownPreviewHandler.csproj

@@ -137,6 +137,9 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="System.IO.Abstractions">
+      <Version>12.2.5</Version>
+    </PackageReference>
   </ItemGroup>
   <ItemGroup>
     <AdditionalFiles Include="..\..\..\codeAnalysis\StyleCop.json">

src/modules/previewpane/MarkdownPreviewHandler/MarkdownPreviewHandlerControl.cs

@@ -4,7 +4,7 @@
 
 using System;
 using System.Drawing;
-using System.IO;
+using System.IO.Abstractions;
 using System.Text.RegularExpressions;
 using System.Windows.Forms;
 using Common;
@@ -21,6 +21,10 @@ namespace Microsoft.PowerToys.PreviewHandler.Markdown
     /// </summary>
     public class MarkdownPreviewHandlerControl : FormHandlerControl
     {
+        private static readonly IFileSystem FileSystem = new FileSystem();
+        private static readonly IPath Path = FileSystem.Path;
+        private static readonly IFile File = FileSystem.File;
+
         /// <summary>
         /// Extension to modify markdown AST.
         /// </summary>