libstdc++: Add more tests for filesystem directory iterators

libstdc++: Add more tests for filesystem directory iterators

The PR 97731 test was added to verify a fix to the Filesystem TS code,
but we should also have the same test to avoid similar regressions in
the C++17 std::filesystem code.

Also add tests for directory_options::follow_directory_symlink

libstdc++-v3/ChangeLog:

	* testsuite/27_io/filesystem/iterators/97731.cc: New test.
	* testsuite/27_io/filesystem/iterators/recursive_directory_iterator.cc:
	Check follow_directory_symlink option.
	* testsuite/experimental/filesystem/iterators/recursive_directory_iterator.cc:
	Likewise.