libstdc++: Fix non-reserved names in headers

libstdc++: Fix non-reserved names in headers

Fix some bad uses of "ForwardIterator" in <ranges>.

There's also a "il" parameter in a std::seed_seq constructor in <random>
which is only reserved since C++14.

libstdc++-v3/ChangeLog:

	* include/bits/random.h (seed_seq(initializer_list<T>)): Rename
	parameter to use reserved name.
	* include/bits/ranges_algo.h (shift_left, shift_right): Rename
	template parameters to use reserved name.
	* testsuite/17_intro/names.cc: Check "il". Do not check "d" and
	"y" in C++20 mode.

(cherry picked from commit 23f75da95f5e8e09e9fcbd5b0d2885e6c44739aa)