Core/Vehicles: Keep vendors seated on player passenger mounts - #32077

Summary

• Traveler's Tundra Mammoth, Grand Expedition Yak, Mighty Caravan Brutosaur, and Trader's Gilded Brutosaur seat their vendors with a control-vehicle aura. The ride spell's target selection was dropping the player mount, and stripping that aura during boarding ran the mammoth goodbye.
• A passenger-cast ride aura is left in place while the vendor is still seated, including the indoor aura check. The mount aura itself still drops indoors.
• Player mounts clear the vehicle record's no-jump and no-strafe flags when the vehicle id is sent and again on dismount.
• Each vendor's board spline is sent with the spawn, then again on its own timer, so the client keeps both passengers.
• Mounts 1039 and 2265 use creatures 9001039 and 9002265 for vehicle 6372. Those creatures are never spawned. Merchant Maku's stock is included.
• Vehicle 6372 keeps the howdah seats but uses the mammoth locomotion flags so strafing turns onto the diagonal.

Still needed

• Vendors board a moment after the mount appears. They do not spawn already sitting in the seat.
• The vehicle 6372 hotfix applies to every user of that vehicle record, not only the player mounts.

Test plan

• Mount Traveler's Tundra Mammoth, Grand Expedition Yak, Mighty Caravan Brutosaur, and Trader's Gilded Brutosaur and confirm both vendors sit and ride.
• Switch among them, and dismount then remount, while the previous vendors are still despawning.
• Eject a vendor, then dismount, and confirm jump and normal ground movement are back.
• Strafe on either brutosaur and confirm the mount turns onto the diagonal instead of sliding with a forward run anim.
• Go indoors and confirm the mount drops without the mammoth vendors running their goodbye early.
• Open Merchant Maku, Killia (auction house), and Melanie Morten (mailbox).