When mobs are slain by withers, they are unable to replace replaceable blocks with wither roses

When mobs are slain by withers, they are unable to replace replaceable blocks such as snow, grass, light blocks, fire etc. with wither roses. Relates to MC-269974.

Steps to reproduce

1. Make sure the gamerule mobGriefing is set to true

2. Place snow

3. Stand in the snow

4. /summon pig ~ ~ ~ {NoAI:1b}

5. /summon minecraft:wither ~ ~ ~ {NoAI:1b}

6. /damage @e[type=pig,limit=1,sort=nearest] 10 minecraft:mob_attack by @e[type=minecraft:wither,limit=1]

Observed: Upon the pig's demise, it doesn't replace the snow with a wither rose; instead, the rose is dropped as an item.

Expected: The pig should replace the snow with a wither rose upon being killed by the wither.