Add causes for TargetInvocationException in TriggerGlobal

[Mailaender]

This addresses #18802 (comment) where a simple typo of a player name causes a large and difficult to read stacktrace.

OpenRA/mods/ra/scripts/campaign.lua

Lines 12 to 15 in 0751b30

	InitObjectives = function(player)
	Trigger.OnObjectiveCompleted(player, function(p, id)
	Media.DisplayMessage(p.GetObjectiveDescription(id), UserInterface.Translate("objective-completed"))
	end)

will crash when the player is null because the function expects a certain type

OpenRA/OpenRA.Mods.Common/Scripting/Global/TriggerGlobal.cs

Lines 179 to 184 in 0751b30

	[Desc("Call a function when this player completes an objective. " +
	"The callback function will be called as func(Player player, int objectiveID).")]
	public void OnObjectiveCompleted(Player player, LuaFunction func)
	{
	GetScriptTriggers(player.PlayerActor).RegisterCallback(Trigger.OnObjectiveCompleted, func, Context);
	}

and the type conversion fails while the script is being loaded, which is also why we don't get line numbers for some reason. This shortens the stacktrace by throwing earlier.

[abcdefg30]

This breaks all script functions that want to pass nil. (See allies-01 or any other usage of reinforcements for example.)

[Mailaender]

It indeed breaks in allies-01 with the second helicopter. My next approach throws even more

 ---> System.NullReferenceException: actor
   at OpenRA.Mods.Common.Scripting.TriggerGlobal.OnKilled(Actor actor, LuaFunction func) in OpenRA/OpenRA.Mods.Common/Scripting/Global/TriggerGlobal.cs:line 88

but adds the method signature to the exception.

[abcdefg30]

Ok.

[PunkPun]

OnAllKilled is missing a null check. Also this should get rebased for easier testing

[PunkPun]

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