libstdc++: Adding missing feature-test macros for C++23 ranges algos

This patch also renames __cpp_lib_fold to __cpp_lib_ranges_fold
as per the current draft standard.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algo.h (__cpp_lib_ranges_contains):
	Define for C++23.
	(__cpp_lib_ranges_iota): Likewise.
	(__cpp_lib_ranges_find_last): Likewise.
	(__cpp_lib_fold): Rename to ...
	(__cpp_lib_ranges_fold): ... this.
	* include/std/version: As above.
	* testsuite/25_algorithms/fold_left/1.cc: Adjust after
	renaming __cpp_lib_fold.
	* testsuite/std/ranges/version_c++23.cc: Verify values
	of the above feature-test macros.