Rollup merge of #110563 - bryangarza:refactor-trait-selection-error-reporting, r=compiler-errors

Break up long function in trait selection error reporting + clean up nearby code

- Move blocks of code into their own functions
- Replace a few function argument types with their type aliases
- Create "AppendConstMessage" enum to replace a nested `Option`.

compiler/rustc_infer/src/traits/mod.rs

@@ -123,7 +123,7 @@ pub struct FulfillmentError<'tcx> {
 #[derive(Clone)]
 pub enum FulfillmentErrorCode<'tcx> {
     /// Inherently impossible to fulfill; this trait is implemented if and only if it is already implemented.
-    CodeCycle(Vec<Obligation<'tcx, ty::Predicate<'tcx>>>),
+    CodeCycle(Vec<PredicateObligation<'tcx>>),
     CodeSelectionError(SelectionError<'tcx>),
     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
     CodeSubtypeError(ExpectedFound<Ty<'tcx>>, TypeError<'tcx>), // always comes from a SubtypePredicate