[rustdoc] Hide items from search but leave it clickable under publiced module

[tesuji]

In #67346, I wanted to hide HashMap from search under hash_map module.

It could be nice to have a way to

• hide items from search but leave it under other publicized module
• display only one in search for items that are re-publiced in multiple modules.

[tesuji]

@rustbot modify labels: T-rustdoc

[GuillaumeGomez]

cc @rust-lang/rustdoc

[GuillaumeGomez]

As for this topic, I have a few options in mind but I think my favorite is:

#[doc(search_hidden)]