WordPress - Show the (next and previous) navigation for post, page and custom post types (CPT). Use `[show_post_navigation]`

show-post-navigation.php

<?php
/**
 * Show the (next and previous) navigation for post, page and custom post types (CPT).
 *
 * @example 	[show_post_navigation]
 * 
 * @todo Change the `prefix_` and with your own unique prefix.
 * 
 * @since 1.0.0
 */
if( ! function_exists( 'prefix_post_navigation' ) ) :
	function prefix_post_navigation( $atts, $content ) {

		if( ! is_singular( ) ) {
			return '';
		}

		$post_obj = get_post_type_object( get_post_type() );

		$next_text = sprintf(
			'Next %s &rarr;',
			$post_obj->labels->singular_name
		);

		$prev_text = sprintf(
			'&larr; Previous %s',
			$post_obj->labels->singular_name
		);

		return get_the_post_navigation( array(
			'next_text' => $next_text,
			'prev_text' => $prev_text,
		) );
   }
   add_shortcode( 'show_post_navigation', 'prefix_post_navigation' );
endif;