libstdc++: Add deprecated attribute to std::random_shuffle declarations

We already have these attributes on the definitions in <bits/stl_algo.h>
but they don't work due to PR c++/84542. Add the attributes to the
declarations in <bits/algorithmfwd.h> as well, and add a test.

libstdc++-v3/ChangeLog:

	* include/bits/algorithmfwd.h (random_shuffle): Add deprecated
	attribute.
	* include/bits/stl_algo.h (random_shuffle): Correct comments.
	* testsuite/25_algorithms/random_shuffle/1.cc: Disable
	deprecated warnings.
	* testsuite/25_algorithms/random_shuffle/59603.cc: Likewise.
	* testsuite/25_algorithms/random_shuffle/moveable.cc: Likewise.
	* testsuite/25_algorithms/random_shuffle/deprecated.cc: New
	test.