Make Language Icons compatible with Drupal 9.x

Add core_version_requirement: ^8 || ^9 to languageicons.info.yml to designate that the theme is compatible with Drupal 9.
See https://www.drupal.org/node/3070687.

drupal-check & rector reports below :-

vendor/bin/rector process web/modules/contrib/languageicons --dry-run
Rector 0.8.x-dev@8896f0a
Config file: rector.yml

 9/9 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

2 files with changes
====================

1) web/modules/contrib/languageicons/languageicons.module

    ---------- begin diff ----------
--- Original
+++ New
@@ -1,4 +1,6 @@
 <?php
+use Drupal\Core\Url;
+use Drupal\Component\Utility\Html;
 /**
  * @file
  * Icons for language links.
@@ -38,7 +40,7 @@
       $output .= '<p>' . t('For more information, please see <a href="@handbook">the online handbook section</a>.', array('@handbook' => 'http://drupal.org/node/133977')) . '</p>';
       return $output;
     case 'admin/config/regional/language/icons':
-      $output = '<p>' . t('To enable multilingual support for specific content types go to <a href="@configure_content_types">configure content types</a>.', array('@configure_content_types' => \Drupal\Core\Url::fromRoute('entity.node_type.collection'))) . '</p>';
+      $output = '<p>' . t('To enable multilingual support for specific content types go to <a href="@configure_content_types">configure content types</a>.', array('@configure_content_types' => Url::fromRoute('entity.node_type.collection'))) . '</p>';
       return $output;
   }
 }
@@ -104,7 +106,7 @@
   if ($path = \Drupal::config('languageicons.settings')->get('path')) {
     $variables['icon'] = [
       '#theme' => 'image',
-      '#uri' => str_replace('*', $language->getId(), \Drupal\Component\Utility\Html::escape($path)),
+      '#uri' => str_replace('*', $language->getId(), Html::escape($path)),
       '#alt' => $title,
       '#title' => $title,
       '#width' => $width,
    ----------- end diff -----------

2) web/modules/contrib/languageicons/src/Form/LanguageiconsAdminSettings.php

    ---------- begin diff ----------
--- Original
+++ New
@@ -40,7 +40,7 @@
     return ['languageicons.settings'];
   }

-  public function buildForm(array $form, \Drupal\Core\Form\FormStateInterface $form_state) {
+  public function buildForm(array $form, FormStateInterface $form_state) {
     $form['show'] = [
       '#type' => 'fieldset',
       '#title' => t('Add language icons'),
    ----------- end diff -----------


 [OK] Rector is done! 2 files would have changed (dry-run).



vendor/bin/drupal-check -ad web/modules/contrib/languageicons
 3/3 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%



 [OK] No errors