Change markdown files to treat soft endings as hard (#11271)

.github/actions/spell-check/expect.txt

@@ -676,6 +676,7 @@ hangeul
 hanja
 hanselman
 hardcoded
+Hardlines
 HARDWAREINPUT
 hashcode
 hbitmap
@@ -1809,6 +1810,7 @@ sln
 SMALLICON
 SMTO
 snd
+softline
 somil
 Soref
 SORTDOWN

src/modules/previewpane/MarkdownPreviewHandler/MarkdownPreviewHandlerControl.cs

@@ -65,9 +65,15 @@ namespace Microsoft.PowerToys.PreviewHandler.Markdown
         /// </summary>
         public MarkdownPreviewHandlerControl()
         {
+            // if you have a string with double space, some people view it as a new line.
+            // while this is against spec, even GH supports this. Technically looks like GH just trims whitespace
+            // https://github.com/microsoft/PowerToys/issues/10354
+            var softlineBreak = new Markdig.Extensions.Hardlines.SoftlineBreakAsHardlineExtension();
             _extension = new HTMLParsingExtension(ImagesBlockedCallBack);
+
             _pipelineBuilder = new MarkdownPipelineBuilder().UseAdvancedExtensions().UseEmojiAndSmiley().UseYamlFrontMatter().UseMathematics();
             _pipelineBuilder.Extensions.Add(_extension);
+            _pipelineBuilder.Extensions.Add(softlineBreak);
         }
 
         /// <summary>