Fix error on death when ACU/SACU drone pods are built without ACU/SACU

[lL1l1]

Issue

If drone pods are built without an ACU/SACU they cause an error on death and don't get cleaned up. This can happen by cheat spawning them or by being built from a factory like in the common "All Faction Quantum Gate" mod.

warning: Error running OnKilled script in Entity uea0003 at 23591f08: ...github\fa\lua\sim\units\uef\tconstructionpodunit.lua(191): attempt to call method `NotifyOfPodDeath' (a nil value)
         stack traceback:
         	...github\fa\lua\sim\units\uef\tconstructionpodunit.lua(191): in function <...github\fa\lua\sim\units\uef\tconstructionpodunit.lua:190>

Description of the proposed changes

• Add a nil check for self.Parent, as the parent only gets set by units specifically scripted to use the pod's SetParent function.
• Intellisense work in related scripts

Testing done on the proposed changes

Spawning pods with the cheat menu no longer causes an error, and they die properly.

Additional context

Curiously, pods are attached to the creator unit through I believe the engine, so they die instantly when cheat spawned or if the creator dies.

Checklist

• Changes are annotated, including comments where useful
• Changes are documented in the changelog for the next game version