(Duplicate) Server animation timeline commands do not run

DUPLICATE OF MCM-708

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Verification builds: 1.13.0.1
Regression builds: 1.12.0.25

Summary: Entity timeline animations do not run commands. In other words, they don't work whatsoever. The controllers themselves work fine; on_entry works, etc. But not commands inside an animation timeline.

Impact: Since server timelines left experimental in 1.12 which is unreleased, no current "live" content is broken by this. It breaks several maps in development.

Repro Steps:

1. Download and open the attached world in 1.12.
2. Spawn a pig and verify it prints "Hello" every second or so.
3. Try again in 1.13.

Expected Results: Same result, pig prints "Hello" every second or so.

Observed Results: Nothing happens.

Screenshots/Videos attached: Yes