Core/Spells: implement DoT clipping

* Core/Spells: Implementation of DoT clipping.
* Core/Utilities: Backport "EnumFlags v3.0" from master.
* Core/Spells: Switch AURA_REMOVE_MODE to a flag set.

src/server/scripts/Spells/spell_hunter.cpp

@@ -557,7 +557,7 @@ class spell_hun_misdirection : public SpellScriptLoader
 
             void OnRemove(AuraEffect const* /*aurEff*/, AuraEffectHandleModes /*mode*/)
             {
-                if (GetTargetApplication()->GetRemoveMode() != AURA_REMOVE_BY_DEFAULT || !GetTarget()->HasAura(SPELL_HUNTER_MISDIRECTION_PROC))
+                if (!GetTargetApplication()->GetRemoveMode().HasFlag(AuraRemoveFlags::ByDefault) || !GetTarget()->HasAura(SPELL_HUNTER_MISDIRECTION_PROC))
                     GetTarget()->ResetRedirectThreat();
             }