Rename many interner functions.

(This is a large commit. The changes to
`compiler/rustc_middle/src/ty/context.rs` are the most important ones.)

The current naming scheme is a mess, with a mix of `_intern_`, `intern_`
and `mk_` prefixes, with little consistency. In particular, in many
cases it's easy to use an iterator interner when a (preferable) slice
interner is available.

The guiding principles of the new naming system:
- No `_intern_` prefixes.
- The `intern_` prefix is for internal operations.
- The `mk_` prefix is for external operations.
- For cases where there is a slice interner and an iterator interner,
  the former is `mk_foo` and the latter is `mk_foo_from_iter`.

Also, `slice_interners!` and `direct_interners!` can now be `pub` or
non-`pub`, which helps enforce the internal/external operations
division.

It's not perfect, but I think it's a clear improvement.

The following lists show everything that was renamed.

slice_interners
- const_list
  - mk_const_list -> mk_const_list_from_iter
  - intern_const_list -> mk_const_list
- substs
  - mk_substs -> mk_substs_from_iter
  - intern_substs -> mk_substs
  - check_substs -> check_and_mk_substs (this is a weird one)
- canonical_var_infos
  - intern_canonical_var_infos -> mk_canonical_var_infos
- poly_existential_predicates
  - mk_poly_existential_predicates -> mk_poly_existential_predicates_from_iter
  - intern_poly_existential_predicates -> mk_poly_existential_predicates
  - _intern_poly_existential_predicates -> intern_poly_existential_predicates
- predicates
  - mk_predicates -> mk_predicates_from_iter
  - intern_predicates -> mk_predicates
  - _intern_predicates -> intern_predicates
- projs
  - intern_projs -> mk_projs
- place_elems
  - mk_place_elems -> mk_place_elems_from_iter
  - intern_place_elems -> mk_place_elems
- bound_variable_kinds
  - mk_bound_variable_kinds -> mk_bound_variable_kinds_from_iter
  - intern_bound_variable_kinds -> mk_bound_variable_kinds

direct_interners
- region
  - intern_region (unchanged)
- const
  - mk_const_internal -> intern_const
- const_allocation
  - intern_const_alloc -> mk_const_alloc
- layout
  - intern_layout -> mk_layout
- adt_def
  - intern_adt_def -> mk_adt_def_from_data (unusual case, hard to avoid)
  - alloc_adt_def(!) -> mk_adt_def
- external_constraints
  - intern_external_constraints -> mk_external_constraints

Other
- type_list
  - mk_type_list -> mk_type_list_from_iter
  - intern_type_list -> mk_type_list
- tup
  - mk_tup -> mk_tup_from_iter
  - intern_tup -> mk_tup

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -572,7 +572,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
         debug_assert!(!out_value.needs_infer() && !out_value.has_placeholders());
 
         let canonical_variables =
-            tcx.intern_canonical_var_infos(&canonicalizer.universe_canonicalized_variables());
+            tcx.mk_canonical_var_infos(&canonicalizer.universe_canonicalized_variables());
 
         let max_universe = canonical_variables
             .iter()

compiler/rustc_infer/src/infer/canonical/mod.rs

@@ -88,7 +88,7 @@ impl<'tcx> InferCtxt<'tcx> {
         universe_map: impl Fn(ty::UniverseIndex) -> ty::UniverseIndex,
     ) -> CanonicalVarValues<'tcx> {
         CanonicalVarValues {
-            var_values: self.tcx.mk_substs(
+            var_values: self.tcx.mk_substs_from_iter(
                 variables
                     .iter()
                     .map(|info| self.instantiate_canonical_var(span, info, &universe_map)),

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -474,8 +474,8 @@ impl<'tcx> InferCtxt<'tcx> {
         // given variable in the loop above, use that. Otherwise, use
         // a fresh inference variable.
         let result_subst = CanonicalVarValues {
-            var_values: self.tcx.mk_substs(query_response.variables.iter().enumerate().map(
-                |(index, info)| {
+            var_values: self.tcx.mk_substs_from_iter(
+                query_response.variables.iter().enumerate().map(|(index, info)| {
                     if info.is_existential() {
                         match opt_values[BoundVar::new(index)] {
                             Some(k) => k,
@@ -488,8 +488,8 @@ impl<'tcx> InferCtxt<'tcx> {
                             universe_map[u.as_usize()]
                         })
                     }
-                },
-            )),
+                }),
+            ),
         };
 
         let mut obligations = vec![];

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -925,7 +925,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     ) -> Option<()> {
         // FIXME/HACK: Go back to `SubstsRef` to use its inherent methods,
         // ideally that shouldn't be necessary.
-        let sub = self.tcx.intern_substs(sub);
+        let sub = self.tcx.mk_substs(sub);
         for (i, ta) in sub.types().enumerate() {
             if ta == other_ty {
                 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, other_ty);