Libc++'s implementation of shuffle and sample already support lvalue and rvalue
RNG's. This patch adds tests for both categories and marks the issue as complete.
This patch also contains drive-by change for std::experimental::sample which
improves the diagnostics produced when the correct iterator categories are
not supplied.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@279947 91177308-0d34-0410-b5e6-96231b3b80d8
