P2328R1 `join_view` Should Join All `view`s Of `range`s

[StephanTLavavej]

P2328R1 join_view Should Join All views Of ranges

No feature-test macro is mentioned.

At the June 2021 virtual plenary meeting, this was accepted as a defect report for C++20, which means that this paper applies retroactively to the C++20 Standard.

[CaseyCarter]

This effectively depends on #1984.

[CaseyCarter]

When implementing this, consider using the non-propagating cache for split_view::_Current which #2012 puts in a _Defaultabox.