Support modified handling with new vehicle model IDs

[ArranTuna]

Is your feature request related to a problem? Please describe.
If a new vehicle model ID is added with engineRequestModel you must create that vehicle with a normal vehicle ID server side and set it on each client to the new ID. But the problem is that changing a vehicle model causes it's handling to be reset. Therefore it's impossible to have synced modified handling because each client is changing the model ID at a different time.

Describe the solution you'd like
For whatever you have set with setVehicleHandling to carry over to the new vehicle ID when you change it client side.

Describe alternatives you've considered

• Calling setVehicleHandling every time a new client changes the ID is obviously infeasible on any busy server since that is data that gets sent out to all clients.
• There is no setVehicleHandling client side either.

Additional context
You'll need a new nightly that has engineRequestModel("vehicle") support.

[Pirulax]

Closing in favor of #1835

It deals with this issue, since it'll allow the model to be allocated server side (thus no hackery needed to use the model client side)