Use an ugly name to help catch field projection

[scottmcm]

Something's happening, based on rust-lang/rust#144621, so go further than before by removing the visibility from the field and having definitions use a from_array method instead where needed.

This is draft because it's absolutely not going to work first try, but I'd like to borrow CI for fixing.

[scottmcm]

Oh, the arm generator is completely different from when I was last here. I have no idea how to add the ::from_array calls...

[folkertdev]

I fixed those here e3ba06b, you can cherry-pick + squash that if you think that looks good.

[scottmcm]

Oh, no wonder I couldn't find it in the Expression stuff 🤦 Thanks for putting that together!

That said, it looks like the problem wasn't in here after all -- it was just a different thing that failed for all SIMD. So I'm going to close this and not do the churn of updating everything, unless people feel that this would be better (in avoiding accidentally adding projections in future) enough to actually go through with doing it everywhere. Thoughts welcome.

[scottmcm]

Actually, wait, I can do this slow-stepped: add from_array, start using it in places, but not insist that everything move over all at once. That's probably worth doing, at least.