Auto merge of #79751 - aDotInTheVoid:json-true-idx, r=jyn514

Auto merge of #79751 - aDotInTheVoid:json-true-idx, r=jyn514

Rustdoc: Use correct def_id for doctree::Import

The default overwrites the crate root, which crashes rustdoc-json.

While investigating this, It turns out somehow, some items are being documented twice. I'm not sure how this is happening but for now, we just make sure they were the same if they have the same id.

[Zulip descussion](https://rust-lang.zulipchat.com/#narrow/stream/266220-rustdoc/topic/Panic.20in.20json-format/near/218899256)

[Bless script](https://gist.github.com/aDotInTheVoid/2dfce0d241338def3f033f941b7c183d) (Once this is more pollished I'll submit it)

r? `@jyn514`