RFC Deprecation descriptions markdowns renderer

[SerafimArts]

type Example {
    field: String @deprecated(reason: """
Because:
- This is an example.
- Because I can!
""")
}

Current behaviour:

\var_dump($field->getDeprecationReason());

// string(...) "Because:\n- This is an example.\n- Because I can!"

Required behaviour:

\var_dump($field->getDeprecationReason());

// string(...) "Because:\n- This is an example.\n- Because I can!"

$renderer = new HtmlRenderer();
\var_dump($field->getDeprecationReason($renderer));

// string(...) "<p>Because:</p><ul><li>This is an example.</li><li>Because I can!</li></ul>"

The method signature must be updated:

public function getDeprecationReason(Renderer $renderer = null): string
{
    return $renderer ? $renderer->render(/* reason */) : /* reason */;
}

Related with:

• RFC Add common mark support #53
• https://github.com/facebook/graphql/blob/e4dae1f2a3e7ba0430b1bc806c345eeeae348e2e/spec/Section%203%20--%20Type%20System.md#deprecated