Mapper::stringToCodeUnits() does not consider "inheritance" between traits

[sebastianbergmann]

test.php

<?php declare(strict_types=1);
require __DIR__ . '/vendor/autoload.php';

use SebastianBergmann\CodeUnit\Mapper;

trait T1
{
    public function one(): void
    {
    }
}

trait T2
{
    use T1;

    public function two(): void
    {
    }
}

class C
{
    use T2;

    public function three(): void
    {
    }
}

$mapper = new Mapper;

foreach ($mapper->stringToCodeUnits(C::class) as $codeUnit) {
    print $codeUnit->name() . PHP_EOL;
}

Actual

C
T2

Expected

C
T2
T1

Originally reported by @InvisibleSmiley in sebastianbergmann/phpunit#6080.