Move m_failed_blocks to ChainstateManager

The member is unrelated to block storage (BlockManager). It is related
to validation.

Fix the confusion by moving it.

Can be reviewed with
--color-moved=dimmed-zebra --color-moved-ws=ignore-all-space

src/validation.h

@@ -405,26 +405,6 @@ private:
 public:
     BlockMap m_block_index GUARDED_BY(cs_main);
 
-    /** In order to efficiently track invalidity of headers, we keep the set of
-      * blocks which we tried to connect and found to be invalid here (ie which
-      * were set to BLOCK_FAILED_VALID since the last restart). We can then
-      * walk this set and check if a new header is a descendant of something in
-      * this set, preventing us from having to walk m_block_index when we try
-      * to connect a bad block and fail.
-      *
-      * While this is more complicated than marking everything which descends
-      * from an invalid block as invalid at the time we discover it to be
-      * invalid, doing so would require walking all of m_block_index to find all
-      * descendants. Since this case should be very rare, keeping track of all
-      * BLOCK_FAILED_VALID blocks in a set should be just fine and work just as
-      * well.
-      *
-      * Because we already walk m_block_index in height-order at startup, we go
-      * ahead and mark descendants of invalid blocks as FAILED_CHILD at that time,
-      * instead of putting things in this set.
-      */
-    std::set<CBlockIndex*> m_failed_blocks;
-
     /**
      * All pairs A->B, where A (or one of its ancestors) misses transactions, but B has transactions.
      * Pruned nodes may have entries where B is missing data.
@@ -909,6 +889,27 @@ public:
     //! chainstate to avoid duplicating block metadata.
     BlockManager m_blockman GUARDED_BY(::cs_main);
 
+    /**
+     * In order to efficiently track invalidity of headers, we keep the set of
+     * blocks which we tried to connect and found to be invalid here (ie which
+     * were set to BLOCK_FAILED_VALID since the last restart). We can then
+     * walk this set and check if a new header is a descendant of something in
+     * this set, preventing us from having to walk m_block_index when we try
+     * to connect a bad block and fail.
+     *
+     * While this is more complicated than marking everything which descends
+     * from an invalid block as invalid at the time we discover it to be
+     * invalid, doing so would require walking all of m_block_index to find all
+     * descendants. Since this case should be very rare, keeping track of all
+     * BLOCK_FAILED_VALID blocks in a set should be just fine and work just as
+     * well.
+     *
+     * Because we already walk m_block_index in height-order at startup, we go
+     * ahead and mark descendants of invalid blocks as FAILED_CHILD at that time,
+     * instead of putting things in this set.
+     */
+    std::set<CBlockIndex*> m_failed_blocks;
+
     //! The total number of bytes available for us to use across all in-memory
     //! coins caches. This will be split somehow across chainstates.
     int64_t m_total_coinstip_cache{0};