Check existing uses of unwrap_usize for ty::Array

[varkor]

Generally, we should be using assert_usize, which will fail gracefully if we have a generic parameter as an array length instead, and handling that case specially. Using unwrap_usize has caused issues in the past: #61380.

ICEs resulting from this issue have the form:

error: internal compiler error: src/librustc/ty/sty.rs:2311: expected constant usize, got Const {
    ty: usize,
    val: Param(
        N/#0,
    ),
}

[yodaldevoid]

unwrap_usize was renamed to eval_usize in commit 9b87d22.

[lcnr]

What's our current status here?

[varkor]

I don't think anyone did a formal triage, but I skimmed through at some point, and there weren't any more worrying uses. It might be safe to close this, and reopen if we hit the same ICE again.

[lcnr]

I also looked over this in the past and didn't see anything obviously incorrect. So let's go ahead with closing this
and and look into this a bit more if it causes another ICE.