Properly escape HTML in every Scribe actions

In recent commits I separated how we could add text in the editor. So
we need to escape HTML in both method that add text:
insertTextInEditor and setTextInEditor.

I had to extract the HTML escape part of
convertTextContentToHtmlContent because when using setTextInEditor we
do not need to convert \n to <br>.

core/lib/utils/string_convert.dart

@@ -251,16 +251,14 @@ class StringConvert {
     }
   }
 
-  static String convertTextContentToHtmlContent(String textContent) {
-    // Escape HTML entities first to prevent interpretation as HTML
-    final escapedContent = textContent
-        .replaceAll('&', '&')
-        .replaceAll('<', '&lt;')
-        .replaceAll('>', '&gt;')
-        .replaceAll('"', '&quot;')
-        .replaceAll("'", '&#39;');
+  static String escapeTextContent(String textContent) {
+    const HtmlEscape htmlEscape = HtmlEscape();
 
-    final htmlContent = escapedContent.replaceAll('\n', '<br>');
+    return htmlEscape.convert(textContent);
+  }
+
+  static String convertTextContentToHtmlContent(String textContent) {
+    final htmlContent = textContent.replaceAll('\n', '<br>');
 
     return '<div>$htmlContent</div>';
   }