Always allow backtick in title, summary and body (#1726)

* Always allow backtick in title, even tho it could interpreted as markdown anotation for text as code

* Also allow backticks in body

* Allow ambigous use of ` in message body

* Fix issue with html code block and still suppot ambigous backticks

Author: axely123

src/Altinn.Correspondence.Common/Helpers/TextValidation.cs

@@ -18,11 +18,13 @@ public static string ConvertToHtml(string markdown)
 
     public static bool ValidatePlainText(string text)
     {
+        // Ignore backticks in the comparison so backticks are always accepted.
+        var normalizedInput = text.Replace("`", "");
         var converter = new ReverseMarkdown.Converter();
-        var markdown = converter.Convert(text);
+        var markdown = converter.Convert(normalizedInput);
         var pipeline = new MarkdownPipelineBuilder().UseAdvancedExtensions().Build();
         var plaintext = Markdown.ToPlainText(markdown, pipeline);
-        return plaintext.Trim() == text.Trim();
+        return plaintext.Trim() == normalizedInput.Trim();
     }
 
     public static bool ValidateMarkdown(string markdown)
@@ -41,8 +43,9 @@ public static bool ValidateMarkdown(string markdown)
         var text = WebUtility.HtmlDecode(WebUtility.HtmlDecode(markdown));
         result = WebUtility.HtmlDecode(WebUtility.HtmlDecode(result));
 
-        //As reversemarkdown makes all code blocks to ` we need to replace ``` with ` and `` with ` to compare the strings
-        return ReplaceWhitespaceAndEscapeCharacters(text.Replace("```", "`").Replace("``", "`")) == ReplaceWhitespaceAndEscapeCharacters(result.Replace("```", "`").Replace("``", "`"));
+        // Ignore backticks in the comparison so backticks are always accepted. 
+        // This is to make the validation consistent with how we allow ambiguous use of * and _ in markdown (lenient markdown validation).
+        return ReplaceWhitespaceAndEscapeCharacters(text.Replace("`", "")) == ReplaceWhitespaceAndEscapeCharacters(result.Replace("`", ""));
     }
 
     public static string ReplaceWhitespaceAndEscapeCharacters(string text)