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)
* Mostly aimed at removing Log/DatabaseEnv includes from other headers
* Fix most packet headers including other packet headers - moved common structures such as ItemInstance to their own files
* Moved SAI function definitions to source files (massive or requiring many different dependencies)
* the idea is to have all collections (toybox, heirlooms, mount and later even battle pets) in one class to make it easier and don't increase size of already big Player and WorldSession class
