fix(DB/SAI): BWL Grethok arcane missiles & immunity flags (#9985)

* prevent interupt & cc

* let the world know the duration index meaning

* make Grethok use correct arcane missiles spell

data/sql/updates/pending_db_world/rev_1641213986609051100.sql

@@ -0,0 +1,9 @@
+INSERT INTO `version_db_world` (`sql_rev`) VALUES ('1641213986609051100');
+
+-- Grethok immunity flags
+UPDATE `creature_template` SET `mechanic_immune_mask` = 33636209 WHERE (`entry` = 12557);
+
+-- Grethok - Update arcane missiles to correct spell id (was using triggered spell)
+DELETE FROM `smart_scripts` WHERE (`entryorguid` = 12557) AND (`source_type` = 0) AND (`id` IN (3));
+INSERT INTO `smart_scripts` (`entryorguid`, `source_type`, `id`, `link`, `event_type`, `event_phase_mask`, `event_chance`, `event_flags`, `event_param1`, `event_param2`, `event_param3`, `event_param4`, `event_param5`, `action_type`, `action_param1`, `action_param2`, `action_param3`, `action_param4`, `action_param5`, `action_param6`, `target_type`, `target_param1`, `target_param2`, `target_param3`, `target_param4`, `target_x`, `target_y`, `target_z`, `target_o`, `comment`) VALUES
+(12557, 0, 3, 0, 0, 0, 80, 2, 16000, 16000, 12000, 12000, 0, 11, 22272, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 'Grethok the Controller - In Combat - Cast \'Arcane Missiles\'');

src/server/game/Spells/SpellMgr.cpp

@@ -5543,7 +5543,7 @@ void SpellMgr::LoadDbcDataCorrections()
     ApplySpellFix({ 17731, 69294 }, [](SpellEntry* spellInfo)
     {
         spellInfo->Effect[1] = SPELL_EFFECT_DUMMY;
-        spellInfo->CastingTimeIndex = 3;
+        spellInfo->CastingTimeIndex = 3; // 500ms
         spellInfo->EffectRadiusIndex[1] = 19; // 18yd instead of 13yd to make sure all cracks erupt
     });
 
@@ -7427,7 +7427,7 @@ void SpellMgr::LoadDbcDataCorrections()
     // Shadow Hunter Vosh'gajin - Hex
     ApplySpellFix({ 16097 }, [](SpellEntry* spellInfo)
     {
-        spellInfo->CastingTimeIndex = 16;
+        spellInfo->CastingTimeIndex = 16; // 1500ms
     });
 
     // Sacred Cleansing