Softbody doesn't collide with plane collider (ground)

[Zireael07]

Godot version:
3.1. alpha 1 (how do I check the exact hash given I didn't build it?)

OS/device including version:
Win 7 x64
Radeon HD 6630M

Issue description:
Softbody goes through ground.

Steps to reproduce:
Place softbody node in scene which has a plane collider serving as ground, see it go through ground.
Mesh applied to softbody doesn't matter. Place said softbody above some other collider (e.g. box shape) and see it work properly.

Minimal reproduction project:

[eon-s]

Planes should not be used as solid colliders.
I think the editor must show a warning when a PhysicsBody's CollisionShape gets a plane assigned (I think is the same for Line).

[Zireael07]

Planes are used in 3D game design as an ultimate "bottom of the world" collider that nothing should ever go through (and that's how I'm using it in my game, there is nothing below the ground)

[eon-s]

I know that the concept of a plane is the ideal for this kind of use, but the physics engine do not like it.
See (or remember) #17893 .

[Chaosus]

As stated in #17893 there should be Quad physic shape support instead. Closed as supersede by #17893.