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_codegen_ssa/src/back/symbol_export.rs

@@ -373,7 +373,7 @@ fn upstream_monomorphizations_provider(
                 ExportedSymbol::Generic(def_id, substs) => (def_id, substs),
                 ExportedSymbol::DropGlue(ty) => {
                     if let Some(drop_in_place_fn_def_id) = drop_in_place_fn_def_id {
-                        (drop_in_place_fn_def_id, tcx.intern_substs(&[ty.into()]))
+                        (drop_in_place_fn_def_id, tcx.mk_substs(&[ty.into()]))
                     } else {
                         // `drop_in_place` in place does not exist, don't try
                         // to use it.

compiler/rustc_codegen_ssa/src/base.rs

@@ -476,7 +476,7 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                     cx.tcx(),
                     ty::ParamEnv::reveal_all(),
                     start_def_id,
-                    cx.tcx().intern_substs(&[main_ret_ty.into()]),
+                    cx.tcx().mk_substs(&[main_ret_ty.into()]),
                 )
                 .unwrap()
                 .unwrap(),

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -783,7 +783,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         };
 
         let extra_args = &args[sig.inputs().skip_binder().len()..];
-        let extra_args = bx.tcx().mk_type_list(extra_args.iter().map(|op_arg| {
+        let extra_args = bx.tcx().mk_type_list_from_iter(extra_args.iter().map(|op_arg| {
             let op_ty = op_arg.ty(self.mir, bx.tcx());
             self.monomorphize(op_ty)
         }));
@@ -1547,7 +1547,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             slot
         } else {
             let layout = cx.layout_of(
-                cx.tcx().intern_tup(&[cx.tcx().mk_mut_ptr(cx.tcx().types.u8), cx.tcx().types.i32]),
+                cx.tcx().mk_tup(&[cx.tcx().mk_mut_ptr(cx.tcx().types.u8), cx.tcx().types.i32]),
             );
             let slot = PlaceRef::alloca(bx, layout);
             self.personality_slot = Some(slot);

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -413,7 +413,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     lhs.layout.ty,
                 );
                 let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
-                let operand_ty = bx.tcx().intern_tup(&[val_ty, bx.tcx().types.bool]);
+                let operand_ty = bx.tcx().mk_tup(&[val_ty, bx.tcx().types.bool]);
                 OperandRef { val: result, layout: bx.cx().layout_of(operand_ty) }
             }