Generate a document that contains links to all documented definitions
namespace Facebook\HHAPIDoc; final class IndexDocumentBuilder {...}
->__construct(DocumentationBuilderContext $context)
->getIndexDocument(): string
->getContext(): DocumentationBuilderContext
->getIndexDocumentMarkdown(): string
->renderPart(string $title, dict<string, Documentable> $entries, (function(string): ?string) $get_path): ?string
->renderToHTML(string $markdown): string