rustdoc: correctly propagate cfgs for glob reexports

[lcian]

This fixes some cases of rustdoc not surfacing the correct required feature combination when using #[cfg(feature = ...)] in combination with glob reexports.

See the example cases included as tests.

Here's the generated HTML for those test cases before this change:

and after:

My understanding is that this was basically an off-by-one type of oversight.
We need to update is_inline before calling get_all_import_attributes to immediately reflect that the outermost import we're processing shall indeed be considered as inline, as it's a glob.
Otherwise, we will end up calling add_without_unwanted_attributes with is_inline == false on the "intermediate" re-export, which will skip propagating its cfgs.

I believe this fixes #96166, even though the description there is not super clear on the exact test case they used (there's a snippet but the author says their code is actually different).

Refs #43781
@rustbot label +F-doc_cfg
@rustbot r? @GuillaumeGomez

[GuillaumeGomez]

This is the expected behaviour as described in the rustdoc book: https://doc.rust-lang.org/rustdoc/write-documentation/re-exports.html?highlight=glob#attributes

Although I don't mind changing it. What do you think @rust-lang/rustdoc-internals ?

[yotamofek]

This change absolutely makes sense to me.
The re-exported item will only be visible if the re-export's cfg's predicate is also up-held.

And I might be missing something, but it seems that according the rustdoc book, the current behaviour is wrong for glob re-exports?

These rules also apply if the item is inlined with a glob re-export:

(BTW, the book also has an instance where it says #[cfg(a, b, c)], but I think it should say #[cfg(all(a, b, c))]?)

[GuillaumeGomez]

Oh you're right. Somehow I read the opposite... Sorry about that @lcian.

And yeah, the book has a typo. Feel free to send a PR, otherwise I'll do it once I'm done with my current work.

[Urgau]

Since the re-export's cfg's predicate must also be up-held for the item to be accessible, the change also makes sense to me.

In general I think the default behavior should be the least surprise and this behavior (with/without #[doc(inline)]) seems a bit surprising to me.