Core/AI: Some more refactoring prep for #19930. CreatureAI::EnterCombat is now called CreatureAI::JustEngagedWith. There's also two new methods on UnitAI, though they're never invoked right now.

src/server/game/Entities/Unit/Unit.cpp

@@ -8266,7 +8266,7 @@ void Unit::SetInCombatState(bool PvP, Unit* enemy)
         if (enemy)
         {
             if (IsAIEnabled)
-                creature->AI()->EnterCombat(enemy);
+                creature->AI()->JustEngagedWith(enemy);
 
             if (creature->GetFormation())
                 creature->GetFormation()->MemberAttackStart(creature, enemy);