Codechange: Build station and depot vehicle lists from shared order lists. (#11676)

The brings some performance advantages:

* No need to iterate all vehicles and check for primary vehicle as only vehicles that can have orders are listed.
* Shared orders only need to be tested once instead of for each vehicle sharing them.
* Vehicle tests only need to be performed on the first shared vehicle instead of all.

Add: precondition checks to functions that work with both valid company and deity

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.

Codechange: use GSCompanyMode::IsValid, IsDeity, and the precondition helpers

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".

Fix: Some Script::IsValidVehicle checks need to be complemented with IsPrimaryVehicle

Add: [Script] ScriptVehicle.IsPrimaryVehicle