fix: avoid hint items shadow local item from completions

[CubeSugarCheese]

Relevant Issues

#18398 Don't auto import items when one is already in scope
#17164 Block specific items from being auto-imported

Fixed Problem

Now completions will not hint item that could shadow local item.

Problems that May Arise

Unexpected behavior

Maybe we can auto rename or use long path to disambiguation, and add a option to control the behavior.

[ChayimFriedman2]

This makes the search N*M, I'd be much happier with a hash set.

[CubeSugarCheese]

This makes the search N*M, I'd be much happier with a hash set.

finish.
During refactoring, I notice that Rustc will treat prelude items and built in types different than normal items.
For prelude, allow shadow by use statement. Like std::result::Result::Ok shadow by use anyhow::Ok. This is not what we want.
For built in types, allow same name item. Like str and core::str, it also allow coexist with user defined item. This feature must support.
Finally, I choose to forbid same items and ignore all built in types. This rule may need to be improved.

[Veykril]

I feel like this should be the responsibility of the caller (doing the filtering), also this needs to be aware of namespaces, we do want to show importing completions for imports that bring a name into scope into a namespace that is currently "empty". (think of importing the Deserialize trait while the derive is already in scope)

[Veykril]

restore this

[bors]

☔ The latest upstream changes (presumably #18699) made this pull request unmergeable. Please resolve the merge conflicts.

[CubeSugarCheese]

Apologies for the late reply. I've realized that the current approach is a bit too simplistic and rough. The specific rules and details still need further discussion. In light of that, I’ve decided to mark this PR as a draft so we can continue to discuss and refine the approach further.