sstables: add intrusive index hook to large_data_record

Add a set_member_hook<auto_unlink> to large_data_record so it can
participate directly in a boost::intrusive::multiset without wrapper
nodes or side maps.  The hook is not listed in describe_type() and
is therefore not serialized.

Also add a non-const get_large_data_records() overload to sstable
so that register_sstable can obtain mutable references to records
for hook manipulation.

sstables/sstables.hh

@@ -1101,6 +1101,10 @@ public:
         return _large_data_records;
     }
 
+    std::optional<scylla_metadata::large_data_records>& get_large_data_records() noexcept {
+        return _large_data_records;
+    }
+
     // Return the extended timestamp statistics map.
     // Some or all entries may be missing if not present in scylla_metadata
     scylla_metadata::ext_timestamp_stats::map_type get_ext_timestamp_stats() const noexcept;

sstables/types.hh

@@ -17,6 +17,7 @@
 #include "mutation/tombstone.hh"
 #include "utils/streaming_histogram.hh"
 #include "utils/estimated_histogram.hh"
+#include <boost/intrusive/set.hpp>
 #include "sstables/key.hh"
 #include "sstables/file_writer.hh"
 #include "db/commitlog/replay_position.hh"
@@ -614,6 +615,11 @@ struct large_data_record {
     uint64_t range_tombstones;              // number of range tombstones in the partition
     uint64_t dead_rows;                     // number of dead rows in the partition
 
+    // Runtime hook for large_data_record_index.  Not serialized.
+    using index_hook_type = boost::intrusive::set_member_hook<
+        boost::intrusive::link_mode<boost::intrusive::auto_unlink>>;
+    index_hook_type _index_hook;
+
     template <typename Describer>
     auto describe_type(sstable_version_types v, Describer f) {
         return f(type, partition_key, clustering_key, column_name, value,