rest_get_date_with_gmt( string $date, bool $is_utc = false )

function rest_get_date_with_gmt( $date, $is_utc = false ) {
	// Whether or not the original date actually has a timezone string
	// changes the way we need to do timezone conversion.  Store this info
	// before parsing the date, and use it later.
	$has_timezone = preg_match( '#(Z|[+-]\d{2}(:\d{2})?)$#', $date );

	$date = rest_parse_date( $date );

	if ( empty( $date ) ) {
		return null;
	}

	// At this point $date could either be a local date (if we were passed a
	// *local* date without a timezone offset) or a UTC date (otherwise).
	// Timezone conversion needs to be handled differently between these two
	// cases.
	if ( ! $is_utc && ! $has_timezone ) {
		$local = date( 'Y-m-d H:i:s', $date );
		$utc = get_gmt_from_date( $local );
	} else {
		$utc = date( 'Y-m-d H:i:s', $date );
		$local = get_date_from_gmt( $utc );
	}

	return array( $local, $utc );
}