refactor(Core/Trainer): Import TC handling of Trainers

[Kitzunu]

• Cherry-pick commit (TrinityCore/TrinityCore@bf3ab6d)

Co-Authored-By: Shauren [email protected]
Co-Authored-By: Ghaster [email protected]

old #5428

Closes #5420

TODO:

• Implement acore::Containers::MapGetValuePtr feat(Core/Containers): MapGetValuePtr #6111
• Implement Cell::VisitWorldObjects refactor(Core/Grids): Ported cmangos/mangos-wotlk@ea99457 #6113
• Implement sSpellMgr->AssertSpellInfo feat(Core/Spell): AssertSpellInfo #6115
• Implement AsUnderlyingType feat(Core/Util): AsUnderlyingType #6117
• Implement SkillLineAbility.dbc to determine player initial spells fix(Core/Player): Use SkillLineAbility.dbc to determine player initia… #6015

[FrancescoBorzi]

Co-Authored-By: Shauren [email protected]
Co-Authored-By: Ghaster [email protected]

[Kitzunu]

LMAO

[Sedatyf]

Sorry about the mention thing, wrong copy paste 😓

[Helias]

This PR will improve the AoWoW compatibility 🚀

[Kitzunu]

too much conflicts