Replace mk_foo calls with infer_foo where possible.

There are several `mk_foo`/`intern_foo` pairs, where the former takes an
iterator and the latter takes a slice. (This naming convention is bad,
but that's a fix for another PR.)

This commit changes several `mk_foo` occurrences into `intern_foo`,
avoiding the need for some `.iter()`/`.into_iter()` calls. Affected
cases:
- mk_type_list
- mk_tup
- mk_substs
- mk_const_list

compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs

@@ -813,21 +813,18 @@ fn transform_substs<'tcx>(
     substs: SubstsRef<'tcx>,
     options: TransformTyOptions,
 ) -> SubstsRef<'tcx> {
-    let substs: Vec<GenericArg<'tcx>> = substs
-        .iter()
-        .map(|subst| {
-            if let GenericArgKind::Type(ty) = subst.unpack() {
-                if is_c_void_ty(tcx, ty) {
-                    tcx.mk_unit().into()
-                } else {
-                    transform_ty(tcx, ty, options).into()
-                }
+    let substs = substs.iter().map(|subst| {
+        if let GenericArgKind::Type(ty) = subst.unpack() {
+            if is_c_void_ty(tcx, ty) {
+                tcx.mk_unit().into()
             } else {
-                subst
+                transform_ty(tcx, ty, options).into()
             }
-        })
-        .collect();
-    tcx.mk_substs(substs.iter())
+        } else {
+            subst
+        }
+    });
+    tcx.mk_substs(substs)
 }
 
 /// Returns a type metadata identifier for the specified FnAbi using the Itanium C++ ABI with vendor