Summary:
Printing file checksum (usually an integer) in non-hex format is barely useful. To make the matter
worse, it can mess with the output format. If you use `less` to redirect the output of `ldb manifest_dump`,
non-hex file checksum can cause `less` not to function as expected.

Also output some additional fields to json output.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9196

Test Plan: manually test `ldb manifest_dump`.

Reviewed By: ajkr

Differential Revision: D32590253

Pulled By: riversand963

fbshipit-source-id: de434b7e60dd05b0b7cb76eff2240b21f9ae4b32