Allow monster spellcasting without a target

[Venera3]

Summary

None

Purpose of change

Spells are great! Monsters only being able to use them when they see an enemy is pretty limiting, so let's change that.

Describe the solution

Added allow_no_target (default false) that lets a monster to cast the spell in question even when they don't see an enemy. The spell will target the monster's own position in that case.

Describe alternatives you've considered

Not doing this.
Adding some fancy targeting so they can e.g. heal up their allies at range even when left alone, but that can come later.

Testing

Added the bool to dermatik_emergence, spawned a poor doggo and watched it get undoggo'd without it noticing me.

Additional context

Setting up as a workaround to #59753 , so no spells using it for now.
Since EOCs are only called on spells by monsters this could potentially be used for a lot of fun mapgen updating like a monster that alters its lair's layout until it gets shanked.

[MNG-cataclysm]

Couldn't this be used with the Triffid Heart? Over time, it could spawn additional root chambers and spawn more monsters.

[Venera3]

Sure, with the pretty big caveat that it would require you to come back into the bubble for it to pop.