Mob spawner doesn't show what mob it's supposed to spawn

^{Update by [Mod] OcelotOnesie:}
Summary:
Mob spawners no longer show the miniature mob inside of them.

Steps to Reproduce:

1. Place down a mob spawner or find a naturally generated one.
2. Use a spawn egg on the spawner.

Observed Results:
The mob is not visible inside of the spawner.

Expected Results:
The mob is visible inside of the spawner.

Screenshots/Videos attached: Yes

Notes:

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Original Description:
Naturally occuring mob spawner doesn't show what mob it's supposed to be.