add ChainstateManager.GetSnapshot{BaseHeight,BaseBlock}()

For use in later commits.

src/validation.h

@@ -869,6 +869,13 @@ private:
     /** Most recent headers presync progress update, for rate-limiting. */
     std::chrono::time_point<std::chrono::steady_clock> m_last_presync_update GUARDED_BY(::cs_main) {};
 
+    //! Returns nullptr if no snapshot has been loaded.
+    const CBlockIndex* GetSnapshotBaseBlock() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+
+    //! Return the height of the base block of the snapshot in use, if one exists, else
+    //! nullopt.
+    std::optional<int> GetSnapshotBaseHeight() const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+
 public:
     using Options = kernel::ChainstateManagerOpts;