Display new image sizes choices set through add_image_size() also in the backend in the right sidebar when editing an image

listing-18-16.php

function wh_add_image_sizes_to_backend( $existingsizes ) {
    $addsizes = array(
        "wh-homepage-teaser"    => 'WH Homepage Teaser',
        "wh-landingpage-stage"  => 'WH Landingpage Stage',
        "wh-detailpage-feature" => 'WH Detailpage Feature'
    );
    $newsizes = array_merge( $existingsizes, $addsizes );
    return $newsizes;
}
add_filter( 'image_size_names_choose', 'wh_add_image_sizes_to_backend' );