2179: Use HirDatabase to compute `is_deprecated` r=matklad a=martskins
This PR fixes#2167 by introducing `attributes_query` and adding `fn attrs(&self, def: crate::AttrDef) -> Option<Arc<[Attr]>>;` to the `DefDatabase` trait.
I'm a little concerned about the two spots in `attributes_query` where code is repeated, but I couldn't figure out a way to avoid that, so.. I welcome suggestions 😄
Co-authored-by: Martin Asquino <martin.asquino@gmail.com>