Use less rustc_type_ir in the compiler codebase

This commit does the following:
 - Replaces use of rustc_type_ir by rustc_middle
 - Removes the rustc_type_ir dependency
 - The DelayedSet type is exposed by rustc_middle so everything can be
   accessed through rustc_middle in a coherent manner.

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -14,9 +14,8 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_hir as hir;
 use rustc_infer::traits::{Obligation, PolyTraitObligation, SelectionError};
 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
-use rustc_middle::ty::{self, Ty, TypeVisitableExt, TypingMode};
+use rustc_middle::ty::{self, Ty, TypeVisitableExt, TypingMode, elaborate};
 use rustc_middle::{bug, span_bug};
-use rustc_type_ir::elaborate;
 use tracing::{debug, instrument, trace};
 
 use super::SelectionCandidate::*;

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -15,10 +15,9 @@ use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::{DefineOpaqueTypes, HigherRankedType, InferOk};
 use rustc_infer::traits::ObligationCauseCode;
 use rustc_middle::traits::{BuiltinImplSource, SignatureMismatchData};
-use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, Upcast};
+use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, Upcast, elaborate};
 use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::DefId;
-use rustc_type_ir::elaborate;
 use thin_vec::thin_vec;
 use tracing::{debug, instrument};
 

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -28,10 +28,9 @@ use rustc_middle::ty::error::TypeErrorToStringExt;
 use rustc_middle::ty::print::{PrintTraitRefExt as _, with_no_trimmed_paths};
 use rustc_middle::ty::{
     self, GenericArgsRef, PolyProjectionPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitableExt,
-    TypingMode, Upcast,
+    TypingMode, Upcast, elaborate,
 };
 use rustc_span::{Symbol, sym};
-use rustc_type_ir::elaborate;
 use tracing::{debug, instrument, trace};
 
 use self::EvaluationResult::*;