VehicleWheel3D Sinks Through Gaps Smaller Than Itself & VehicleBody3D Slides on Slopes

### Tested versions

4.3-stable

I'm pretty sure this is the case across all Godot 4 versions. Not sure about Godot 3.

### System information

System info not needed.

### Issue description

When you drive a VehicleBody3D through a gap smaller than its wheels, they sink down and get stuck. Sometimes forever, and then you have to restart the game.

When you drive a VehicleBody3D to a slope, then brake, it's supposed to stay like that. In this case however, it slides down until it's on a perfectly flat surface, then loses momentum and stops.

I've thought of reporting these separately but since these nodes are related, I think it's fine.

Changing physics engine to Jolt or Rapier does not fix these issues.

### Steps to reproduce

1- Download the project and open it up.
2- Press play. You can drive the vehicle with WASD or Arrow keys and look around with the mouse.
3- Drive towards the higher slope right in front of you. Then stop driving. Vehicle slides down, which is not realistic. You can hold Space key while doing it to apply the brakes and watch it slowly slide down.
4- Drive towards the lower slopes and drive slowly over them. I don't know how to describe what will happen.

### Minimal reproduction project (MRP)

[vehiclebody_sliding_down.zip](https://github.com/user-attachments/files/17336343/vehiclebody_sliding_down.zip)

Open vehiclebody_sliding_down.zip and run the reproduction project as described, testing the VehicleBody3D and VehicleWheel3D behavior on the slopes and gaps. Compare the results with the Godot, Jolt, and Rapier physics options mentioned in the report. Done means the vehicle no longer sinks into smaller gaps or slides down slopes after braking.

Written by the indexing model from the issue text.