Rename declaration_name -> display_name

Declaration names sounds like a name of declaration -- something you
can use for analysis. It empathically isn't, and is just a label
displayed in various UI. It's important not to confuse the two, least
we accidentally mix semantics with UI (I believe, there's already a
case of this in the FamousDefs at least).

crates/assists/src/utils.rs

@@ -406,7 +406,7 @@ pub use prelude::*;
         let std_crate = path.next()?;
         let std_crate = if self
             .1
-            .declaration_name(db)
+            .display_name(db)
             .map(|name| name.to_string() == std_crate)
             .unwrap_or(false)
         {