Write Tests for API Examples of `snack_bar.0`, `elevated_button.0`, `stepper.0`, `radio.0`, `filled_button.0`, `outlined_button.0` & `card.0`
Part of #130459
Fixes#119401
This PR is to:
* add `Card.filled` and `Card.outlined` factory methods so that we can use tokens for these two types of cards to generate default theme instead of providing hard-corded values in example.
* update card.2.dart example.
* add test file for card.2.dart example.
* fix some mismatch caused by editing the auto-generated defaults by hand in navigation_bar.dart and navigation_drawer.dart.