Physics: Add debug inertia view

[carolhmj]

Closes #13775

An example in one of our PGs:

[bjsplat]

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[bjsplat]

Snapshot stored with reference name:
refs/pull/13853/merge

Test environment:
https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13853/merge/index.html

To test a playground add it to the URL, for example:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13853/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/13853/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/13853/merge
https://gui.babylonjs.com/?snapshot=refs/pull/13853/merge
https://nme.babylonjs.com/?snapshot=refs/pull/13853/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/13853/merge#BCU1XR#0

[sebavan]

LGTM, but will wait on @RaananW or @CedricGuillemet review :-)

[CedricGuillemet]

Tested ok with centerOfMassPG. Code looks good but I'm wondering if the display itself is self explanatory.
Inertia is like a core inside (or outside) the shape. Having its display like a collision shape is misleading to me.
Can you please try to replace the wire box display by a scaled sphere ? The idea would be to make the inertia matrix appear like a heavy-solid core inside the physics body.

[RaananW]

Looks great! I have the same comment as Cedric - I am not sure how to understand the visuals. How do I understand inertia from the box?

[CedricGuillemet]

LGTM after discussing with @carolhmj