Without this PR, there is no [reasonable] way to get the following data
for any XBlocks in the new runtime; now there is :)
* index_dictionary: data about the block content, for search indexing
* student_view_data: data-only equivalent of student_view, for use in
custom UIs/mobile
* children: list of child IDs
* editable_children: list of child IDs in the same bundle (use case:
when showing an OLX editor you want to allow editing the OLX of
children in the same bundle but not linked children)
9f6b3a873f