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/scripts/Pet/pet_mage.cpp

@@ -158,7 +158,7 @@ class npc_pet_mage_mirror_image : public CreatureScript
                 owner->CastSpell(me, SPELL_MAGE_CLONE_ME, false);
             }
 
-            void EnterCombat(Unit* who) override
+            void JustEngagedWith(Unit* who) override
             {
                 if (me->GetVictim() && !me->GetVictim()->HasBreakableByDamageCrowdControlAura(me))
                 {