btrfs-progs: Add inode item rebuild function.

btrfs-progs: Add inode item rebuild function.

Add a basic inode item rebuild function for I_ERR_NO_INODE_ITEM.
The main use case is to repair btrfs which fs root has corrupted leaf,
but it is already working for case if the corrupteed fs root leaf/node
contains no inode extent_data.

The repair needs 3 elements for inode rebuild:
1. inode number
   This is quite easy, existing inode_record codes will detect it quite
   well.

2. inode type
   This is the trick part. The only reliable method is to recovery it from
   parent's dir_index/item.
   The remaining method will search for regular file extent for FILE
   type or child's backref for DIR(todo).
   Fallback will be FILE.

Inode name(inode_ref) will be recoverd by nlink repair function.

This is just a fundamental implement, some advanced recovery can be
improved later with btrfs-progs infrastructure change.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>