Rollup merge of #69370 - RalfJung:const-eval-mod, r=oli-obk

move const_eval.rs into the module folder

This groups the file together with the other `const_eval` files in editors, diff views, etc.

r? @oli-obk
diff --git a/src/librustc_mir/const_eval.rs b/src/librustc_mir/const_eval/mod.rs
similarity index 100%
rename from src/librustc_mir/const_eval.rs
rename to src/librustc_mir/const_eval/mod.rs