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_mir_transform/src/shim.rs

@@ -147,7 +147,7 @@ fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>)
     assert!(!matches!(ty, Some(ty) if ty.is_generator()));
 
     let substs = if let Some(ty) = ty {
-        tcx.intern_substs(&[ty.into()])
+        tcx.mk_substs(&[ty.into()])
     } else {
         InternalSubsts::identity_for_item(tcx, def_id)
     };
@@ -597,7 +597,7 @@ fn build_call_shim<'tcx>(
         let untuple_args = sig.inputs();
 
         // Create substitutions for the `Self` and `Args` generic parameters of the shim body.
-        let arg_tup = tcx.intern_tup(untuple_args);
+        let arg_tup = tcx.mk_tup(untuple_args);
 
         (Some([ty.into(), arg_tup.into()]), Some(untuple_args))
     } else {
@@ -632,7 +632,7 @@ fn build_call_shim<'tcx>(
             Adjustment::Deref => tcx.mk_imm_ptr(fnty),
             Adjustment::RefMut => tcx.mk_mut_ptr(fnty),
         };
-        sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
+        sig.inputs_and_output = tcx.mk_type_list(&inputs_and_output);
     }
 
     // FIXME(eddyb) avoid having this snippet both here and in
@@ -643,7 +643,7 @@ fn build_call_shim<'tcx>(
         let self_arg = &mut inputs_and_output[0];
         debug_assert!(tcx.generics_of(def_id).has_self && *self_arg == tcx.types.self_param);
         *self_arg = tcx.mk_mut_ptr(*self_arg);
-        sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
+        sig.inputs_and_output = tcx.mk_type_list(&inputs_and_output);
     }
 
     let span = tcx.def_span(def_id);