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/AI/SmartScripts/SmartAI.cpp

@@ -603,7 +603,7 @@ void SmartAI::JustReachedHome()
     mJustReset = false;
 }
 
-void SmartAI::EnterCombat(Unit* enemy)
+void SmartAI::JustEngagedWith(Unit* enemy)
 {
     if (IsAIControlled())
         me->InterruptNonMeleeSpells(false); // must be before ProcessEvents