Rustdoc-Json: Large Amount of unreferenced `core` in `index`

[aDotInTheVoid]

#![no_std]
pub fn foo() {}

Has an enormous output, that includes core::fmt::Write, and many other unreferenced items.

Many of these items also have dangling Id's.

Possibly caused by #101105

@rustbot modify labels: +A-rustdoc-json +T-rustdoc

[aDotInTheVoid]

Turn out the actual culprit is adding extra trait impls:

rust/src/librustdoc/json/mod.rs

Line 273 in 1463688

index.extend(self.get_trait_items());

Removing this fixes all tests for jsondoclint, and fails none of the current tests, but I thinks thats more of an inditement of the test suite than anything else.

[aDotInTheVoid]

Fixed by #128385 (CC @its-the-shrimp).

The output index now only contains 2 items, the module and the function.