Given the ID of a product in woocommerce, how can I get its URL?

Products in WooCommerce are a custom post type, so this should work:

$url = get_permalink( $product_id );

You can treat that $product_id as a postID (that’s what it is), so you can use it with other normal WP functions, like:

echo '<a href="'.get_permalink($product_id).'">'.get_the_title($product_id).'</a>';