Add div tag with markdown style when isTextTable is true for email content text/plain

Signed-off-by: dab246 <tdvu@linagora.com>

core/lib/presentation/utils/html_transformer/text/persist_preformatted_text_transformer.dart

@@ -1,12 +1,18 @@
 import 'dart:convert';
 
 import 'package:core/presentation/utils/html_transformer/base/text_transformer.dart';
+import 'package:core/utils/html/html_template.dart';
+import 'package:core/utils/string_convert.dart';
 
 class PersistPreformattedTextTransformer extends TextTransformer {
   const PersistPreformattedTextTransformer();
 
   @override
   String process(String text, HtmlEscape htmlEscape) {
-    return '<pre>$text</pre>';
+    if (StringConvert.isTextTable(text)) {
+      return '<div style="${HtmlTemplate.markDownAndASCIIArtStyleCSS}">$text</div>';
+    } else {
+      return text;
+    }
   }
 }

core/lib/utils/html/html_template.dart

@@ -216,4 +216,6 @@ class HtmlTemplate {
       }
      </style>
   ''';
+
+  static const String markDownAndASCIIArtStyleCSS = 'display: block; font-family: monospace; white-space: pre; margin: 1em 0px;';
 }