Check cancellation when updating imports recursively

For winapi, this takes a lot of CPU time without doing queries and
causes the main event loop to stall on cancellation.

crates/ra_hir_def/src/nameres/collector.rs

@@ -573,6 +573,7 @@ fn update(
         vis: Visibility,
         import_type: ImportType,
     ) {
+        self.db.check_canceled();
         self.update_recursive(module_id, resolutions, vis, import_type, 0)
     }