make example font_atlas_debug deterministic with a seeded random

[mockersf]

Objective

• Make example font_atlas_debug deterministic so that it's easier to check for regression

Solution

• Use a seeded random

[james7132]

If this is meant to be an example for new users, wouldn't this be confusing why we're using a seeded RNG? I can see the benefit in CI but this seems to be a regression in explainability.

[pablo-lua]

I can see the benefit in CI but this seems to be a regression in explainability.

I agree, we can at least explain that we are using seeded rng for ci reasons somewhere (we have something like this in the gizmos_axes example, after explanation, I understood why we are using this, but I don't think a beginner will understand without we saying anything)

[mockersf]

to be fair, I think the other solution is to remove the example font_atlas_debug because it's of no use for users, it was meant to debug how atlas are built for fonts

[alice-i-cecile]

Determinism is generally useful in games: I'm okay with showing users how to do it, if they happen to be poking through this mostly-internal example.

[james7132]

Probably raised this in the wrong PR, since this one is meant for debug, but examples like alien cake addict (in #12515) probably deserves more mention as to why we choose to set it up that way.