[victoriafalls] Move the block to lba translation to a small wrapper.

Abstract this away into a thin wrapper over the denali client such that
it can be called from other helper classes.

sys/victoriafalls/fs/ext2/ext2_block_reader.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <denali/denali_client.h>
+#include <glacier/status/error_or.h>
+#include <mammoth/memory_region.h>
+
+#include "fs/ext2/ext2.h"
+
+class Ext2BlockReader {
+ public:
+  static glcr::ErrorOr<Ext2BlockReader> Init(ScopedDenaliClient&& denali);
+
+  Superblock* GetSuperblock();
+  uint64_t SectorsPerBlock();
+
+  glcr::ErrorOr<MappedMemoryRegion> ReadBlock(uint64_t block_number);
+  glcr::ErrorOr<MappedMemoryRegion> ReadBlocks(uint64_t block_number,
+                                               uint64_t num_blocks);
+
+ private:
+  ScopedDenaliClient denali_;
+  MappedMemoryRegion super_block_region_;
+
+  Ext2BlockReader(ScopedDenaliClient&& denali, MappedMemoryRegion super_block);
+};