Use InstantArticleInterface instead of InstantArticle as parameter type for Transformer methods

[radamou]

Steps required to reproduce the problem

1. for public function transformString($context, $content, $encoding = "utf-8"), replace $context Type (from InstantArticle to InstantArticle Interface)

2. public function transformString(InstantArticleInterface $context, string $content, string $encoding = "utf-8")

Expected Result

• public function transformString(InstantArticleInterface $context, string $content, string $encoding = "utf-8")

Actual Result