[3.3.5] Combat/Threat rewrite - prep & refactor (#19966)

* Combat/Threat rewrite (PR #19930) prep work. Mostly refactors, and a compatibility layer on ThreatManager/HostileReference that allows scripts to be changed already.

src/server/scripts/Spells/spell_generic.cpp

@@ -4653,9 +4653,9 @@ class spell_gen_blink : public SpellScriptLoader
                 {
                     if (Creature* caster = GetCaster()->ToCreature())
                     {
-                        if (HostileReference* ref = caster->getThreatManager().getCurrentVictim())
+                        if (Unit* target = caster->GetThreatManager().GetCurrentVictim())
                         {
-                            ref->setThreat(0.0f);
+                            caster->GetThreatManager().ResetThreat(target);
                             if (caster->IsAIEnabled)
                             {
                                 caster->CastSpell(target, SPELL_BLINK_TARGET, true);