[3.3.5] CastSpell unclusterfucking (that's a word now) (#21123)

Core/Spell: The giant CastSpell unclusterfucking (that's a word now) of this generation.

- CastSpell now always takes three arguments - target, spellId, and a struct containing extra arguments
- This struct (CastSpellExtraArgs, see SpellDefines.h) serves as a conglomerate of every previous combination of the 20 billion different CastSpell overloads, all merged into one
  - It has some great utility constructors - check them out! All of these can be used to implicitly construct the ExtraArgs object.
- A gajillion refactors to make everything behave the way it always has

(cherry picked from commit d507a7e338)

src/server/game/Handlers/TradeHandler.cpp

@@ -509,10 +509,10 @@ void WorldSession::HandleAcceptTradeOpcode(WorldPackets::Trade::AcceptTrade& acc
         trader->ModifyMoney(my_trade->GetMoney());
 
         if (my_spell)
-            my_spell->prepare(&my_targets);
+            my_spell->prepare(my_targets);
 
         if (his_spell)
-            his_spell->prepare(&his_targets);
+            his_spell->prepare(his_targets);
 
         // cleanup
         clearAcceptTradeMode(my_trade, his_trade);