views_get_page_view() and views_set_page_view()

In order to make views renderable views_get_page_view() and views_set_page_view() have been replaced by
\Drupal\views\Plugin\views\display\Page::getPageRenderArray() and \Drupal\views\Plugin\views\display\Page::setPageRenderArray()

This allows you to still access the current view ID and display ID, using #view_id and #display_id If you need any information from it, you though have to manually load the view, using
\Drupal\views\View::getView() for example.
One important detail is that it no longer contains the executed view, by design, of render caching. Render caching happens in a way that even the inititial view is not loaded.