1. Create a course with studen s1
2. Create h5pactivity with Embed on
3. Add a page activity. Insert embed code from previous activity
4. Back up and restore course into new course2 (include enrolled users)
5. Enrol another student s2 into a course2
6. Access page activity

Expected: Both students can see h5p in page activity
Actual: Only student s1 can see h5p in page activity

The underlying problem is that the embedding code for mod_h5pactivity uses a pluginfile.php url that is urlencoded and hence is not modified by backup/restore process.

Example: http://localhost/h5p/embed.php?url=http%3A%2F%2Flocalhost%2Fpluginfile.php%2F24%2Fmod_h5pactivity%2Fpackage%2F0%2Finteractive-content-29523.h5p&component=mod_h5pactivity

will be encoded to 
$@H5PEMBED@$?url=http%3A%2F%2Flocalhost%2Fpluginfile.php%2F24%2Fmod_h5pactivity%2Fpackage%2F0%2Finteractive-content-29523.h5p&component=mod_h5pactivity

The patch takes care of that and enhances backup_course_task::encode_links_helper() and restore_decode_rule accordingly for possible later use in other cases as there are other activities that might need similar encoding.