Avoid re-interning in LateContext::get_def_path

The def path printer in `get_def_path` essentially calls
`Symbol::intern(&symbol.to_string())` for simple symbols in a path.
This accounts for ~30% of the runtime of get_def_path.

We can avoid this by simply appending the symbol directly when available.

Author: DaniPopes

compiler/rustc_lint/src/context.rs

@@ -812,7 +812,10 @@ impl<'tcx> LateContext<'tcx> {
                     return Ok(());
                 }
 
-                self.path.push(Symbol::intern(&disambiguated_data.data.to_string()));
+                self.path.push(match disambiguated_data.data.get_opt_name() {
+                    Some(sym) => sym,
+                    None => Symbol::intern(&disambiguated_data.data.to_string()),
+                });
                 Ok(())
             }