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-exports, which will skip propagating their 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