Add HighlightModifier::Callable and add it for locals

crates/ide/src/syntax_highlighting.rs

@@ -763,6 +763,9 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
             if local.is_mut(db) || local.ty(db).is_mutable_reference() {
                 h |= HighlightModifier::Mutable;
             }
+            if local.ty(db).as_callable(db).is_some() {
+                h |= HighlightModifier::Callable;
+            }
             return h;
         }
     }