Make BlockManager::LoadBlockIndex private

Summary:
BlockManager::LoadBlockIndex is only called by BlockManager::LoadBlockIndexDB. Thus, it can be made private.
m_best_invalid is no longer accessed by BlockManager::LoadBlockIndex. Thus, the unused friend can be removed.

This is a backport of [[bitcoin/bitcoin#24917 | core#24917]]

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D13070

Author: MarcoFalke

src/node/blockstorage.h

@@ -69,6 +69,13 @@ class BlockManager {
     friend ChainstateManager;
 
 private:
+    /**
+     * Load the blocktree off disk and into memory. Populate certain metadata
+     * per index entry (nStatus, nChainWork, nTimeMax, etc.) as well as
+     * peripheral collections like m_dirty_blockindex.
+     */
+    bool LoadBlockIndex(const Consensus::Params &consensus_params)
+        EXCLUSIVE_LOCKS_REQUIRED(cs_main);
     void FlushBlockFile(bool fFinalize = false, bool finalize_undo = false);
     void FlushUndoFile(int block_file, bool finalize = false);
     bool FindBlockPos(FlatFilePos &pos, unsigned int nAddSize,
@@ -143,14 +150,6 @@ class BlockManager {
     bool WriteBlockIndexDB() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
     bool LoadBlockIndexDB() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
-    /**
-     * Load the blocktree off disk and into memory. Populate certain metadata
-     * per index entry (nStatus, nChainWork, nTimeMax, etc.) as well as
-     * peripheral collections like m_dirty_blockindex.
-     */
-    bool LoadBlockIndex(const Consensus::Params &consensus_params)
-        EXCLUSIVE_LOCKS_REQUIRED(cs_main);
-
     /** Clear all data members. */
     void Unload() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 

src/validation.h

@@ -1093,7 +1093,6 @@ class ChainstateManager {
 
     CBlockIndex *m_best_invalid;
     CBlockIndex *m_best_parked;
-    friend bool node::BlockManager::LoadBlockIndex(const Consensus::Params &);
 
     //! Internal helper for ActivateSnapshot().
     [[nodiscard]] bool