Codechange: [Script] Use helper function over direct casting CompanyID

In the script's API `COMPANY_INVALID` has a value of -1, whereas the internal
game's `INVALID_COMPANY` has a value of 255. Since the script's API also has
a `COMPANY_SPECTATOR` with a value of 255, these enumerations cannot be easily
reconciled by casting. As such, replace all casts in the script API with
either ScriptCompany::FromScriptCompanyID or ScriptCompany::ToScriptCompanyID.

Also make clear whether CompanyID is ::CompanyID or ScriptCompany::CompanyID
by using either one of those over CompanyID in the script's API.

src/script/api/script_controller.cpp

@@ -67,7 +67,7 @@
 	ScriptLog::Log(error_msg ? ScriptLogTypes::LOG_SQ_ERROR : ScriptLogTypes::LOG_SQ_INFO, message);
 }
 
-ScriptController::ScriptController(CompanyID company) :
+ScriptController::ScriptController(::CompanyID company) :
 	ticks(0),
 	loaded_library_count(0)
 {