py/objstr: Split mp_obj_str_from_vstr into bytes/str versions.

Previously the desired output type was specified.  Now make the type part
of the function name.  Because this function is used in a few places this
saves code size due to smaller call-site.

This makes `mp_obj_new_str_type_from_vstr` a private function of objstr.c
(which is almost the only place where the output type isn't a compile-time
constant).

This saves ~140 bytes on PYBV11.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/objint.c

@@ -446,7 +446,7 @@ STATIC mp_obj_t int_to_bytes(size_t n_args, const mp_obj_t *args) {
         mp_binary_set_int(l, big_endian, data + (big_endian ? (len - l) : 0), val);
     }
 
-    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
+    return mp_obj_new_bytes_from_vstr(&vstr);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(int_to_bytes_obj, 3, 4, int_to_bytes);