Fix libc++.natvis visualizers for std::__Cr::set, map, multimap, and multiset

How tested: used Visual Studio to successfully dump the contents of a
std::__Cr::multimap. The other objects also use the same tree object and
receive the same changes.

The changes around __compressed_pair are needed due to, I believe, this:
https://source.chromium.org/chromium/_/chromium/external/github.com/llvm/llvm-project/libcxx/+/6dbcc4ce783b564853aa58f9532ac1dc3ca37297

For the ValueNode, I did not track down when/where __cc_ became invalid,
but it did not work unless I removed it.

Change-Id: Iec502916aa8850f3fc0541418085ea7dbba6b74b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6838869
Reviewed-by: Nico Weber <thakis@chromium.org>
Auto-Submit: Erik Anderson <Erik.Anderson@microsoft.com>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1500126}