7110: Deduplicate macros when offering completion r=matklad a=AdnoC
Closes https://github.com/rust-analyzer/rust-analyzer/issues/7081
When iterating over the names within the `hir_def::resolver::Scope` for a module, track what macros are in the `hir_def::item_scope::ItemScope::legacy_macros` collection for the module. When iterating over names from the prelude, do not proccess the name if it had been in the `legacy_macros` collection.
This is implemented with a `FxHashSet` in the `Scope::process_names` function that is populated when iterating over `legacy_macros` and checked when iterating over the prelude.
Alternative implementation could instead query the `legacy_macros` `FxHashMap` directly when processing names in the prelude.
Also, I'd like to add a test for this, but I'm not sure where it could be added.
Co-authored-by: AdnoC <adam.r.cutler@gmail.com>
