Fixes to php depreciations and warnings

[skriptxadmin]

Fix for following warnings and notices

PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\admin\class-h5p-content-admin.php on line 179
PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\admin\class-h5p-library-admin.php on line 52
PHP Deprecated:  Creation of dynamic property H5PWordPress::$plugin_slug is deprecated in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\public\class-h5p-wordpress.php on line 74
PHP Warning:  Undefined property: stdClass::$patch_version_in_folder_name in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\h5p-editor-php-library\h5peditor.class.php on line 633
PHP Deprecated:  Optional parameter $results declared before required parameter $limit is implicitly treated as a required parameter in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\admin\class-h5p-content-query.php on line 400
PHP Deprecated:  Optional parameter $offset declared before required parameter $limit is implicitly treated as a required parameter in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\admin\class-h5p-content-query.php on line 400
PHP Deprecated:  json_decode(): Passing null to parameter #1 ($json) of type string is deprecated in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\admin\class-h5p-editor-wordpress-storage.php on line 113
PHP Deprecated:  explode(): Passing null to parameter #2 ($string) of type string is deprecated in C:\xampp\htdocs\xxx\wp-content\plugins\h5p\admin\class-h5p-content-admin.php on line 875

Fix Reference: https://stackoverflow.com/questions/69207368/constant-filter-sanitize-string-is-deprecated