The default functionality within the `ThemeSupport` class has an unintended
side-effect of breaking the existing default functionality within the
`wc_get_theme_support()` function. Since the default set in the support
class is prioritized over the one given to `ThemeSupport::get_option()`,
the WordPress options set in the Customizer are never used for images.
- New class class-wc-twenty-twenty-one.php
- New stylesheet twenty-twenty-one.scss
- Updates checks for default themes in theme_support_includes() and wc_is_wp_default_theme_active()