NextAction refactoring to eliminate sentinel arrays and pointers (#1923)

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# Description

This PR aims to refactor the NextAction declaration to achieve two
goals:

## Eliminate C-style sentinel arrays

Currently, a double pointer (`NextAction**`) approach is being used.
This an old pre-C++11 (< 2011) trick before `std::vector<>` became a
thing.
This approach is painful for developers because they constantly need to
declare their `NextAction` arrays as:
```cpp
NextAction::array(0, new NextAction("foo", 1.0f), nullptr)
```
Instead of:
```cpp
{ new NextAction("foo", 1.0f) }
```
The first argument of `NextAction::array` is actually a hack. It is used
to have a named argument so `va_args` can find the remaining arguments.
It is set to 0 everywhere but in fact does nothing. This is very
confusing to people unfamiliar with this antiquated syntax.
The last argument `nullptr` is what we call a sentinel. It's a `nullptr`
because `va_args` is looking for a `nullptr` to stop iterating. It's
also a hack and also leads to confusion.

## Eliminate unnecessary pointers for `NextAction`

Pointers can be used for several reasons, to cite a few:
- Indicate strong, absolute identity.
- Provide strong but transferable ownership (unlike references).
- When a null value is acceptable (`nullptr`).
- When copy is expensive.

`NextAction` meets none of these criteria:
- It has no identity because it is purely behavioural.
- It is never owned by anything as it is passed around and never fetched
from a registry.
- The only situations where it can be `nullptr` are errors that should
in fact throw an `std::invalid_argument` instead.
- They are extremely small objects that embark a single `std::string`
and a single `float`.

Pointers should be avoided when not strictly necessary because they can
quickly lead to undefined behaviour due to unhandled `nullptr`
situations. They also make the syntax heavier due to the necessity to
constantly check for `nullptr`. Finally, they aren't even good for
performance in that situation because shifting a pointer so many times
is likely more expensive than copying such a trivial object.

# End goal

The end goal is to declare `NextAction` arrays this way:
```cpp
{ NextAction("foo", 1.0f) }
```

> [!NOTE]
> Additional note: `NextAction` is nothing but a hacky proxy to an
`Action` constructor. This should eventually be reworked to use handles
instead of strings. This would make copying `NextAction` even cheaper
and remove the need for the extremely heavy stringly typed current
approach. Stringly typed entities are a known anti-pattern so we need to
move on from those.

src/strategy/Engine.cpp

@@ -258,48 +258,45 @@ ActionNode* Engine::CreateActionNode(std::string const name)
         return node;
 
     return new ActionNode(name,
-                          /*P*/ nullptr,
-                          /*A*/ nullptr,
-                          /*C*/ nullptr);
+                          /*P*/ {},
+                          /*A*/ {},
+                          /*C*/ {});
 }
 
-bool Engine::MultiplyAndPush(NextAction** actions, float forceRelevance, bool skipPrerequisites, Event event,
-                             char const* pushType)
+bool Engine::MultiplyAndPush(
+    std::vector<NextAction> actions,
+    float forceRelevance,
+    bool skipPrerequisites,
+    Event event,
+    char const* pushType
+)
 {
     bool pushed = false;
-    if (actions)
+
+    for (NextAction nextAction : actions)
     {
-        for (uint32 j = 0; actions[j]; j++)
+        ActionNode* action = this->CreateActionNode(nextAction.getName());
+
+        this->InitializeAction(action);
+
+        float k = nextAction.getRelevance();
+
+        if (forceRelevance > 0.0f)
         {
-            if (NextAction* nextAction = actions[j])
-            {
-                ActionNode* action = CreateActionNode(nextAction->getName());
-                InitializeAction(action);
-
-                float k = nextAction->getRelevance();
-                if (forceRelevance > 0.0f)
-                {
-                    k = forceRelevance;
-                }
-
-                if (k > 0)
-                {
-                    LogAction("PUSH:%s - %f (%s)", action->getName().c_str(), k, pushType);
-                    queue.Push(new ActionBasket(action, k, skipPrerequisites, event));
-                    pushed = true;
-                }
-                else
-                {
-                    delete action;
-                }
-
-                delete nextAction;
-            }
-            else
-                break;
+            k = forceRelevance;
         }
 
-        delete[] actions;
+        if (k > 0)
+        {
+            this->LogAction("PUSH:%s - %f (%s)", action->getName().c_str(), k, pushType);
+            queue.Push(new ActionBasket(action, k, skipPrerequisites, event));
+            pushed = true;
+
+            continue;
+        }
+
+        delete action;
+
     }
 
     return pushed;
@@ -530,10 +527,10 @@ std::vector<std::string> Engine::GetStrategies()
 
 void Engine::PushAgain(ActionNode* actionNode, float relevance, Event event)
 {
-    NextAction** nextAction = new NextAction*[2];
-    nextAction[0] = new NextAction(actionNode->getName(), relevance);
-    nextAction[1] = nullptr;
+    std::vector<NextAction> nextAction = { NextAction(actionNode->getName(), relevance) };
+
     MultiplyAndPush(nextAction, relevance, true, event, "again");
+
     delete actionNode;
 }
 
@@ -563,6 +560,13 @@ bool Engine::ListenAndExecute(Action* action, Event event)
 {
     bool actionExecuted = false;
 
+    if (action == nullptr)
+    {
+        LOG_ERROR("playerbots", "Action is nullptr");
+
+        return actionExecuted;
+    }
+
     if (actionExecutionListeners.Before(action, event))
     {
         actionExecuted = actionExecutionListeners.AllowExecution(action, event) ? action->Execute(event) : true;