Allow zdb -r to understand object ids as well

[allanjude]

Sponsored-by: Klara, Inc.
Sponsored-By: Wasabi Technology, Inc.

Motivation and Context

Previously I created: zdb -r pool/dataset path/to/file /tmp/recover.dat

But it turns out, if there is a problem with a directory, you might want to recover a file by its inode number instead

Description

If the argument is a number, thread it as the object-id instead of a filename

How Has This Been Tested?

Manually

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.