libstdc++: Implement LWG 3549 changes to ranges::enable_view

libstdc++: Implement LWG 3549 changes to ranges::enable_view

This patch also reverts r11-3504 since that workaround is now obsolete
after this resolution.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_base.h (view_interface): Forward declare.
	(__detail::__is_derived_from_view_interface_fn): Declare.
	(__detail::__is_derived_from_view_interface): Define as per LWG 3549.
	(enable_view): Adjust as per LWG 3549.
	* include/bits/ranges_util.h (view_interface): Don't derive from
	view_base.
	* include/std/ranges (filter_view): Revert r11-3504 change.
	(transform_view): Likewise.
	(take_view): Likewise.
	(take_while_view): Likewise.
	(drop_view): Likewise.
	(drop_while_view): Likewise.
	(join_view): Likewise.
	(lazy_split_view): Likewise.
	(split_view): Likewise.
	(reverse_view): Likewise.
	* testsuite/std/ranges/adaptors/sizeof.cc: Update expected sizes.
	* testsuite/std/ranges/view.cc (test_view::test_view): Remove
	this default ctor since views no longer need to be default initable.
	(test01): New test.