ufs2: Fix porentially uninited use of fName field

At the same time make it in line with ext2 module

Change-Id: Iab879cf532cbc0b58b23cdd97d50419c21d199b6
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6849
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

ufs2: implementing open_dir and read_dir function

Root directory is read sucessfully.

Change-Id: I8bdc8c1a52edb679a6cb4b5f70e7f42eb2b2c8f1
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2907
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

ufs2: Implementing read_stat function and fs_info

Change-Id: I337c53c017f00f480af7ac94a5774b39eb5255db
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2773
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

ufs2: Reading inodes of ufs2.

Now file system can be mounted sucessfully.

Adding documentation for using the code.

Change-Id: I2bd1b72e06ffc3b5f6306aaa69c59becf4cb882b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2696
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

Move DeviceOpener class to a separate file.

It is used by several of the filesystems, so it seems a good idea to
move it to the shared/ directory.

UFS2, BFS, XFS, EXT2 and EXFAT are adjusted.

Change-Id: I493e37a1e7d3ae24251469f82befd985a3c1dbdd
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2489
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

ufs2: Add superblock, volume, identify() and mount()

Change-Id: I27a492145fe1a365ceea6d172e332167513f5c3b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2381
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>