rustdoc: Built-in macros are not documented in all the necessary locations

NOTE: Some cases below assume #63056 has landed.

❎ https://doc.rust-lang.org/nightly/core/default/index.html doesn't contain the derive macro Default.
✔️ Compare with the https://doc.rust-lang.org/nightly/std/fmt/index.html page which contains the derive macro Debug because it's introduced through a reexport rather than directly.
❎ Some built-in macros not available through the libcore root are documented in the root instead (e.g. derives) - https://doc.rust-lang.org/nightly/core/index.html.
✔️ libcore prelude is documented correctly https://doc.rust-lang.org/nightly/core/prelude/v1/index.html
❎ https://doc.rust-lang.org/nightly/std/default/trait.Default.html doesn't contain the derive macro Default.
❎ Note that https://doc.rust-lang.org/nightly/std/fmt/index.html doesn't contain the derive macro Debug as well.
❎ Derive and attribute macros in libstd prelude https://doc.rust-lang.org/nightly/std/prelude/v1/index.html has to be marked with #[doc(hidden)] currently because otherwise they generate dead links failing the linkchecker testing.
As a result they do not appear on the page.
What is worse, due to #[doc(hidden)] some traits with names matching derives (e.g. Default) are also not documented at that location.

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