[cpp/lua] Split player and mob pet spawn bindings

[MowFord]

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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?

Inching closer towards perfect (and resolving #5495) this PR splits the :spawnPet() function to only handle player entities, and moves the mob logic into a different function that only prepares a pet for summoning. Logic to report incorrect usage:

This PR should have a net behavior change of zero. Except perhaps that the copyconfrontation is moved out of requiring a petid when preparing a mob's pet. It's possible there's some edge case resolved by this, but I would imagine the only thing affected would have been summoner pets, which already pass a petid.

Steps to test these changes

• Go to smn, pup, bst, drg mobs, see they still summon pets
  • note that bst mobs were getting a death listener to remove their pet if it isn't engaged, this is not necessary as of this PR
• be those jobs yourself, see you can still summon pets

[MowFord]

One regression i noticed with this is that pets spawn all around the mob, instead of behind them as before. Going to push a quick update to fix that

Edit: done. Will move this spawn position logic into xi.mob.callPets on the next iteration

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