Disable or fix physics axis locking, as current architecture won't work

[sorenhan]

The Plinko board in the physics functional test takes advantage of axis locking to run in 2d. This doesn't work if MRE is not world-aligned.

Suggested solution

1. remove the ability to do axis locking on X/Y/Z individually, and only support rotation lock (all axes) or position lock (all axes)
2. implement system that enforces y=up on MRE placement, and we can then lock vertical and Horizontal position and rotation.
3. Offer real constraints (which may be expensive, and a lot of work).

Solution 1 is the quickest, 2 would add functionality, but would apply global assumptions about unity physics axes. 3 adds a perf cost

Implementing Solution 1 or 2 would require replacing Plinko with another test, 3 is the only one that would enable Plinko to work

I'd recommend implementing solution 1

[eanders-ms]

Thought: In Unity we may be able to implement these constraints as a configurable joint.