fix(DB/Creatures): Nat Pagle should display vendor icon if player completed Nat's Measuring Tap quest. (#10657)

Moved c++ script to DB. Original author: @offl
Fixes #10559

src/server/game/Entities/Unit/Unit.cpp

@@ -20099,6 +20099,11 @@ void Unit::BuildValuesUpdate(uint8 updateType, ByteBuffer* data, Player* target)
                         appendValue &= ~UNIT_NPC_FLAG_SPELLCLICK;
                     }
 
+                    if (!target->CanSeeVendor(creature))
+                    {
+                        appendValue &= ~UNIT_NPC_FLAG_VENDOR_MASK;
+                    }
+
                     if (!creature->IsValidTrainerForPlayer(target, &appendValue))
                     {
                         appendValue &= ~UNIT_NPC_FLAG_TRAINER;

src/server/game/Entities/Unit/Unit.h

@@ -527,7 +527,9 @@ enum NPCFlags : uint32
     UNIT_NPC_FLAG_GUILD_BANKER          = 0x00800000,       // TITLE is guild banker DESCRIPTION cause client to send 997 opcode
     UNIT_NPC_FLAG_SPELLCLICK            = 0x01000000,       // TITLE has spell click enabled DESCRIPTION cause client to send 1015 opcode (spell click)
     UNIT_NPC_FLAG_PLAYER_VEHICLE        = 0x02000000,       // TITLE is player vehicle DESCRIPTION players with mounts that have vehicle data should have it set
-    UNIT_NPC_FLAG_MAILBOX               = 0x04000000        // TITLE is mailbox
+    UNIT_NPC_FLAG_MAILBOX               = 0x04000000,       // TITLE is mailbox
+
+    UNIT_NPC_FLAG_VENDOR_MASK           = UNIT_NPC_FLAG_VENDOR | UNIT_NPC_FLAG_VENDOR_AMMO | UNIT_NPC_FLAG_VENDOR_POISON | UNIT_NPC_FLAG_VENDOR_REAGENT
 };
 
 enum MovementFlags