Currently, there're (at least) three bugs in the piecewise_construct_t constructor of repeat_view:

1. It can be ambiguous with the internal constructor it uses when constructing repeat_view from empty braces.
2. The internal constructor it uses contains an unqualified call to _Tuple_get, which can cause hard error when used with some ADL-unfriendly types.
3. It constructs the sentinel with _STD make_from_tuple<_Bo>(_Bound_args), where a std::move cast specified by [range.repeat.view]/5 is missing.

This PR removes the internal constructor and introduces a _Make_box_from_tuple function template that emulates std::make_from_tuple to implement [range.repeat.view]/5 more closely to the standard wording. Namespace-qualification and move are also added.

Fixes #5387.