chore: move SSA checks to a new folder (#5434)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

This PR separates read-only checks on the SSA from the passes which
modify it as part of the compilation process.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_evaluator/src/ssa.rs

@@ -36,6 +36,7 @@ use self::{
 };
 
 mod acir_gen;
+mod checks;
 pub(super) mod function_builder;
 pub mod ir;
 mod opt;

compiler/noirc_evaluator/src/ssa/checks/mod.rs

@@ -0,0 +1 @@
+mod check_for_underconstrained_values;

compiler/noirc_evaluator/src/ssa/opt/mod.rs

@@ -7,7 +7,6 @@ mod array_set;
 mod as_slice_length;
 mod assert_constant;
 mod bubble_up_constrains;
-mod check_for_underconstrained_values;
 mod constant_folding;
 mod defunctionalize;
 mod die;