Eliminate `const_field` query

[oli-obk]

Followup to #67901

I think we only have one use site of const_field left:

rust/src/librustc_codegen_ssa/mir/constant.rs

Line 69 in 7f65393

let field = bx.tcx().const_field(

and it iterates over all fields anyway. So we can call destructure_const instead and iterate over the resulting fields.

There should be no more results for searching const_field in the rust source after this, so some comments may need updating to mentioning destructure_const instead of const_field.

These mentoring instructions are a bit vague, I do realize that, so if you encounter any hickup of any magnitude, don't hesitate to write here or contact me via discord/zulip.

This issue has been assigned to @rakshith-ravi via this comment.

[rakshith-ravi]

@rustbot claim

[RalfJung]

destructure_const

I don't think "destructure" is a word. The term I have seen for that (and the term that is commonly used for this operation in the theorem prover community) is "destruct".

EDIT: Okay, it is a word. Still, to me "destruct" sounds better. But maybe that's just because I am used to theorem provers?