Remove PHP dependancy to build langpacks

Currently we're using PHP to build app langpacks, this is slow in CI so it's better if we can remove this dependancy.

Tasks:

1. Auto generate json language files in https://github.com/moodlehq/moodle-local_moodlemobileapp. Already done using github actions. This will use PHP.
2. Update update_lang.sh file to update_langpacks.sh that will:
   1. Download the generated langpacks on task 1.
   2. Select strings needed by the current app.
   3. Detect translated languages and include them into the config.
   4. Generate the local translation module.
   5. Override individual english language files using gulp.