[PP-1] Add array type declaration to parameters in RendererInterface::render()

Problem/Motivation

Passing NULL as the $elements value in RendererInterface::render(&$elements, $is_root_call) was deprecated in 🐛 Fatal error when passing NULL to Renderer::render() Active . This issue is a follow-up to add type declarations to the method parameters, so that the method signature becomes

RendererInterface::render(&$elements, $is_root_call).

Note: since the method signature is being changed, it might be a good time to add a return type declaration of \Drupal\Component\Render\MarkupInterface|string as well.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet