Fix rustdoc not correctly showing attributes on re-exports

[JonathanBrouwer]

Fixes attributes not being shown correctly in rustdoc on re-exports

Does this need to be backported to beta?

r? @jdonszelmann

[rustbot]

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[lolbinarycat]

Maybe could use a comment on the test, but I think its simple enough to be self-explanatory.

I've looked through AttributeKind and there's nothing there that seems like it should be hidden only when an item is inlined, with the possible exception of doc(inline) itself, although the code suggests that the doc attribute isn't using the new attribute parsing system yet.

[JonathanBrouwer]

@lolbinarycat
I've added a comment to the test.

I've matched the fixed behaviour exactly to the old behaviour, which is right above the changed lines.
In the old behaviour, only cfg_trace is excluded. cfg_trace has not been converted to the new attribute parser yet so that's why I put a FIXME in place

[lolbinarycat]

In the old behaviour, only cfg_trace is excluded

both doc and cfg_trace have special handling, and both of them will need that special handling ported to the new system when they are ported to the new system, but that's an issue for a future PR.