[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/PetHandler.cpp

@@ -387,7 +387,7 @@ void WorldSession::HandlePetActionHelper(Unit* pet, ObjectGuid guid1, uint32 spe
                     }
                 }
 
-                spell->prepare(&(spell->m_targets));
+                spell->prepare(spell->m_targets);
             }
             else
             {
@@ -713,7 +713,7 @@ void WorldSession::HandlePetCastSpellOpcode(WorldPackets::Spells::PetCastSpell&
         spellPrepare.ServerCastID = spell->m_castId;
         SendPacket(spellPrepare.Write());
 
-        spell->prepare(&targets);
+        spell->prepare(targets);
     }
     else
     {