A DestinationID is either a DepotID or StationID, where the aircraft hangar
being conceptually a depot is actually a StationID. When making those types
stronger, a lot of casts would need to be added, but this shows the intent
much better.
This allows cargo packets and cargo flow data to be empty if not in use, which is the case for the majority of station goods entries, and data is allocated when needed.
This reduces the initial size of a Station from 9192 bytes to 2024 bytes (on 64 bit platforms), although an allocation of 120 bytes is made for each active cargo type at a station.
Based on similar changes in JGRPP.
These are functions that either use ScriptObject::Command or ScriptObject::GetCompany.
This is a bit over-protective, but having the check everywhere makes it easier to
validate that no check is missing automatically instead of by review.
At this moment these checks will not do anything useful, as either IsValid or
IsDeity from ScriptCompanyMode returns true, but that will change later.
Direct 1:1 replacements in the code, and comments now refer to either
GSCompanyMode::IsValid or GSCompanyMode::IsDeity instead of several variations
on "company mode active" or "no company mode active".
