Auto merge of #152449 - GuillaumeGomez:rustdoc-bang-attr-macro, r=lolbinarycat,mejrs

rustdoc: properly support macros with multiple kinds



Since it seems like I can't reopen https://github.com/rust-lang/rust/pull/145458, opening this one. Although, it's the same PR minus the last new commit to handle a comment that was left unresolved in the original PR. All relevant details are still in the original PR though.

It's an alternative (and likely a take-over) of https://github.com/rust-lang/rust/pull/148005 since lang-team rejected the idea to add documentation on macro branches, making the multiple files approach less suitable.

This implements rust-lang/rust#145153 in rustdoc. This PR voluntarily doesn't touch anything related to intra-doc links, I'll send a follow-up if needed.

So now about the implementation itself: this is a weird case where a macro can be different things at once but still only gets one file generated. I saw two ways to implement this:
1. Handle `ItemKind::Macro` differently and iter through its `MacroKinds` values.
2. Add new placeholder variants in the `ItemKind` enum, which means that when we encounter them in rendering, we need to ignore them. It also makes the `ItemKind` enum bigger (and also needs more code to be handled). Another downside is that it needs to be handled in the JSON output.

Now there was an interesting improvement that came with this PR in the `html::render::print_item::item_module` function: I simplified its implementation and split the different parts in a `HashMap` where the key is the item type. So then, we can just iterate through the keys and open/close the section at each iteration instead of keeping an `Option<section>` around.

From RFCs:
* https://github.com/rust-lang/rust/pull/144579
* https://github.com/rust-lang/rust/pull/145208

derive:

<img width="442" height="327" alt="Screenshot From 2026-04-18 03-11-40" src="https://github.com/user-attachments/assets/f69587a0-8a2b-4080-bc8a-b63dd18f21c1" />

attr:

<img width="442" height="327" alt="Screenshot From 2026-04-18 03-11-31" src="https://github.com/user-attachments/assets/bf9b235a-9d2f-435c-a91e-167562df6b68" />

both:

<img width="442" height="327" alt="Screenshot From 2026-04-18 03-11-50" src="https://github.com/user-attachments/assets/b7e8b3c6-eb99-495b-bdf9-17ba8fb4da0d" />

r? @notriddle