Rollup merge of #125483 - workingjubilee:move-transform-validate-to-mir-transform, r=oli-obk

compiler: validate.rs belongs next to what it validates

It's hard to find code that is deeply nested and far away from its callsites, so let's move `rustc_const_eval::transform::validate` into `rustc_mir_transform`, where all of its callers are. As `rustc_mir_transform` already depends on `rustc_const_eval`, the added visible dependency edge doesn't mean the dependency tree got any worse.

This also lets us unnest the `check_consts` module.

I did look into moving everything inside `rustc_const_eval::transform` into `rustc_mir_transform`. It turned out to be a much more complex operation, with more concerns and real edges into the `const_eval` crate, whereas this was both faster and more obvious.

Author: matthiaskrgr

clippy_utils/src/qualify_min_const_fn.rs

@@ -6,7 +6,7 @@
 use clippy_config::msrvs::{self, Msrv};
 use hir::LangItem;
 use rustc_attr::StableSince;
-use rustc_const_eval::transform::check_consts::ConstCx;
+use rustc_const_eval::check_consts::ConstCx;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;