Integrated BlobDB for backup/restore support (#8129)

Summary:
Add support for blob files for backup/restore like table files.
    Since DB session ID is currently not supported for blob files (there is no place to store it in
    the header), so for blob files uses the
    kLegacyCrc32cAndFileSize naming scheme even if
    share_files_with_checksum_naming is set to kUseDbSessionId.

Pull Request resolved: facebook/rocksdb#8129

Test Plan: Add new test units

Reviewed By: ltamasi

Differential Revision: D27408510

Pulled By: akankshamahajan15

fbshipit-source-id: b27434d189a639ef3e6ad165c61a143a2daaf06e
Signed-off-by: Changlong Chen <levisonchen@live.cn>

env/file_system.cc

@@ -83,6 +83,14 @@ FileOptions FileSystem::OptimizeForCompactionTableRead(
   return optimized_file_options;
 }
 
+FileOptions FileSystem::OptimizeForBlobFileRead(
+    const FileOptions& file_options,
+    const ImmutableDBOptions& db_options) const {
+  FileOptions optimized_file_options(file_options);
+  optimized_file_options.use_direct_reads = db_options.use_direct_reads;
+  return optimized_file_options;
+}
+
 IOStatus WriteStringToFile(FileSystem* fs, const Slice& data,
                            const std::string& fname, bool should_sync) {
   std::unique_ptr<FSWritableFile> file;