Deprecate escaping in display_name_with_default

- Remove escaping in display_name_with_default
- Move escaped version to deprecated display_name_with_default_escaped
- Does not include any other changes to remove double-escaping

Thanks to agaylard who initiated this work:
https://github.com/edx/edx-platform/pull/10756

TNL-3425

cms/templates/widgets/header.html

@@ -38,7 +38,7 @@
         <span class="sr">${_("Current Course:")}</span>
         <a class="course-link" href="${index_url}">
           <span class="course-org">${context_course.display_org_with_default | h}</span><span class="course-number">${context_course.display_number_with_default | h}</span>
-          <span class="course-title" title="${context_course.display_name_with_default}">${context_course.display_name_with_default}</span>
+          <span class="course-title" title="${context_course.display_name_with_default_escaped}">${context_course.display_name_with_default_escaped}</span>
         </a>
       </h2>
 
@@ -141,7 +141,7 @@
         <span class="sr">${_("Current Library:")}</span>
         <a class="course-link" href="${index_url}">
           <span class="course-org">${context_library.display_org_with_default | h}</span><span class="course-number">${context_library.display_number_with_default | h}</span>
-          <span class="course-title" title="${context_library.display_name_with_default}">${context_library.display_name_with_default}</span>
+          <span class="course-title" title="${context_library.display_name_with_default_escaped}">${context_library.display_name_with_default_escaped}</span>
         </a>
       </h2>