[lua] BST mobs pets despawn if not aggresive on master death

[sruon]

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• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Attaches listeners on mobskill "Call Beast" usage, ensuring their pet gets despawned if not aggressive at the time of master death/despawn. See retail example

This ensures pets are not "orphaned" if the master was killed in one hit or despawned due to other conditions (Fomor Beastmaster in Wajaom disappearing during the day, for example)

Steps to test these changes

https://www.youtube.com/watch?v=RJwZFLgiVFs

• Aggro a BST mob and kill it, pet should not despawn
• One shot or !despawnmob a BST mob, the pet should despawn