- For the threaded resolver backend on Windows, revert back to
  exclusively use the threaded resolver with libcurl-owned threading
  instead of GetAddrInfoExW with Windows-owned threading.

Winsock (the Windows sockets library) has a bug where it does not wait
for all of the name resolver threads it is managing to terminate before
returning from WSACleanup. The threads continue to run and may cause a
crash.

This commit is effectively a revert of several commits that encompass
all GetAddrInfoExW code in libcurl. A manual review of merge conflicts
was used to resolve minor changes that had modified the code for
aesthetic or build reasons in other commits.

Prior to this change if libcurl was built with the threaded resolver
backend for Windows, and Windows 8 or later was the operating system at
runtime, and the caller was not impersonating another user, then libcurl
would use GetAddrInfoExW to handle asynchronous name lookups.

GetAddrInfoExW support was added in a6bbc87, which preceded 8.6.0, and
prior to that the threaded resolver backend used libcurl-owned threading
exclusively on Windows.

Reported-by: Ionuț-Francisc Oancea
Reported-by: Razvan Pricope

Ref: https://developercommunity.visualstudio.com/t/ASAN:-heap-use-after-free-in-NdrFullPoin/10654169

Fixes curl#13509 (comment)
Closes #xxxx

---

Revert "asyn-thread: avoid using GetAddrInfoExW with impersonation"

This reverts commit 0caadc1.

Conflicts:
	lib/system_win32.c

--

Revert "asyn-thread: fix curl_global_cleanup crash in Windows"

This reverts commit 428579f.

--

Revert "system_win32: fix a function pointer assignment warning"

This reverts commit 26f002e.

--

Revert "asyn-thread: use GetAddrInfoExW on >= Windows 8"

This reverts commit a6bbc87.

Conflicts:
	lib/asyn-thread.c
	lib/system_win32.c

--