Forward PHPUnit Polyfills path constant to bootstrap file

Author: schlessera

templates/plugin-bootstrap.mustache

@@ -16,6 +16,12 @@ if ( ! $_tests_dir ) {
 	$_tests_dir = rtrim( sys_get_temp_dir(), '/\\' ) . '/wordpress-tests-lib';
 }
 
+// Forward custom PHPUnit Polyfills configuration to PHPUnit bootstrap file.
+$_phpunit_polyfills_path = getenv( 'WP_TESTS_PHPUNIT_POLYFILLS_PATH' );
+if ( false !== $_phpunit_polyfills_path ) {
+	define( 'WP_TESTS_PHPUNIT_POLYFILLS_PATH', $_phpunit_polyfills_path );
+}
+
 if ( ! file_exists( "{$_tests_dir}/includes/functions.php" ) ) {
 	echo "Could not find {$_tests_dir}/includes/functions.php, have you run bin/install-wp-tests.sh ?" . PHP_EOL; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
 	exit( 1 );