PlayerSAO/LocalPlayer refactor: (#4612)

* Create UnitSAO, a common part between PlayerSAO & LuaEntitySAO
* Move breath to PlayerSAO & LocalPlayer
* Migrate m_yaw from (Remote)Player & LuaEntitySAO to UnitSAO
* Migrate m_yaw from Player to LocalPlayer for client
* Move some functions outside of player class to PlayerSAO/RemotePlayer or LocalPlayer depending on which class needs it
* Move pitch to LocalPlayer & PlayerSAO
* Move m_position from Player to LocalPlayer
* Move camera_barely_in_ceiling to LocalPlayer as it's used only there
* use PlayerSAO::m_base_position for Server side positions
* remove a unused variable
* ServerActiveObject::setPos now uses const ref
* use ServerEnv::loadPlayer unconditionnaly as it creates RemotePlayer only if it's not already loaded
* Move hp from Player to LocalPlayer
* Move m_hp from LuaEntitySAO to UnitSAO
* Use m_hp from PlayerSAO/UnitSAO instead of RemotePlayer