Upstream entity links are not deleted if parent block is deleted.

[navinkarkera]

The upstream entity links are not deleted for children blocks that are part of a parent block that is deleted as XBLOCK_DELETED signal is only emitted for the block that is deleted and not for its children. This is also true for index data as it also depends on XBLOCK_DELETED signal.

[navinkarkera]

@bradenmacdonald @ChrisChV I noticed this bug while working on openedx/frontend-app-authoring#2386

[bradenmacdonald]

Thanks! I added it to #37427

[navinkarkera]

Deleting children index data is easier by using breadcrumbs field: b703f2e

[bradenmacdonald]

@navinkarkera Nice! I can review once that's included in a PR. Can you please also update the breadcrumbs field description to indicate that it sometimes has usage_key values too? Right now it only mentions display_name, which is the only required field, but we do but usage_key in there too for non-root items.