Core/Auras: reworked multiplicative AuraEffects calculation

- Splitted containers for flat modifiers and pct modifiers, as they now have different handling
- Amount is now multiplied only on apply; on unapply, iterate through auras and reset the counter
- Fixes many cases of rounding error due to applying/unapplying of small factors
- Allows amounts to be zeroed (ie with an AuraEffect of amount -100)
- Do a partial revert of 6dc37a9add, auras should update amounts only for items allowed (ie no more giving crit to a sword while having an axe in the other hand and being Poleaxe spec'd)
- SPELL_AURA_MOD_SCALE now scales additively, rather than multiplicatively (checked in sniffs)

Closes #18687

src/server/game/Entities/Object/Object.cpp

@@ -806,13 +806,6 @@ void Object::ApplyModSignedFloatValue(uint16 index, float  val, bool apply)
     SetFloatValue(index, cur);
 }
 
-void Object::ApplyPercentModFloatValue(uint16 index, float val, bool apply)
-{
-    float value = GetFloatValue(index);
-    ApplyPercentModFloatVar(value, val, apply);
-    SetFloatValue(index, value);
-}
-
 void Object::ApplyModPositiveFloatValue(uint16 index, float  val, bool apply)
 {
     float cur = GetFloatValue(index);