Add link shortcode to widget title

functions.php

<?php
//* Add link shortcode to widget title
//* Usage: [link href = https://www.google.com]Google[link]
add_filter( 'widget_title', 'link_widget_title' );
function link_widget_title( $title ) { 
    $title = str_replace( '[link', '<a', $title );
    $title = str_replace( '[/link]', '</a>', $title );
    $title = str_replace( ']', '>', $title );

    return $title;
}