querier: switch to v2 compactor output

The change is mostly mechanical: update all compactor instances to the
_v2 variant and update all call-sites, of which there is not that many.
As a consequence of this patch, queries -- both single-partition and
range-scans -- now do the v2->v1 conversion in the consumers, instead of
in the compactor.

test/boost/querier_cache_test.cc

@@ -45,7 +45,7 @@ public:
         _ck = cr.key();
         return stop_iteration::no;
     }
-    stop_iteration consume(range_tombstone&& rt) {
+    stop_iteration consume(range_tombstone_change&& rtc) {
         return stop_iteration::no;
     }
     stop_iteration consume_end_of_partition() {