Collision detection between moving KinematicBody nodes is broken

[e344fde6bf]

Godot version:
3.2.3.stable

OS/device including version:
Arch Linux

Issue description:

When KinematicBody nodes test for collisions, they test against the positions objects had at the start of the physics frame. This causes problems when they are both moving as they can end up overlapping without detecting any collisions. Here is a proposal that discusses this issue in more detail.

Steps to reproduce:

Place two cubes next to each other and use move_and_collide() towards the same position on the same physics frame. This is what happens:

Minimal reproduction project:

test-collision.zip

[madmiraal]

Duplicate of #30481.