Get the title of any page in Drupal 8

functions.php

<?php
            $title = $this->titleResolver->getTitle($route_request, $route_match->getRouteObject());

            // Many paths return a translatable markup object.
            if ($title instanceof TranslatableMarkup) {

              // Sets the title to the translated string.
              $title = $title->render();
            }

            // Other paths, such as admin/structure/menu/manage/main, will
            // return a render array suitable to render using core's XSS filter.
            elseif (is_array($title) && array_key_exists('#markup', $title) && array_key_exists('#allowed_tags', $title)) {
              // Sets the title to the XSS filtered string.
              $title = Xss::filter($title['#markup'], $title['#allowed_tags']);
            }
?>