CBD-6348: [BP] Changes required for folly v2022.02.14.00

This is a cherry-pick from trinity, but the ChangeID is changed
to allow linking with the tlm change

Folly v2022.02.14.00 has removed the method getUniquePtr(), replaced
with as_lock().

Unfortunately our previous version of folly (v2020.09.07.00) did not
yet have the as_lock() function, so we cannot update kv_engine in
advance of the folly update - we must change the method in lock-step
with the upgrade.

Change-Id: If7fd9aea96f4c23092009a985d0ad0d839aac596
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/234760
Reviewed-by: Trond Norbye <[email protected]>
Well-Formed: Restriction Checker
Tested-by: Trond Norbye <[email protected]>

Author: daverigby

programs/engine_testapp/mock_server.cc

@@ -252,7 +252,7 @@ cb::engine_errc mock_waitfor_cookie(const CookieIface* cookie) {
     // Using at() here as the cookie should have been registered in
     // cookieNotifications when it was created.
     auto locked = cookieNotifications.lock();
-    cookieNotificationSignal.wait(locked.getUniqueLock(), [&locked, cookie] {
+    cookieNotificationSignal.wait(locked.as_lock(), [&locked, cookie] {
         return !locked->at(cookie).empty();
     });
     auto& notificationQueue = (*locked)[cookie];