xfs: Enable -Werror, fix all warnings

Define a dedicated OnDiskData structure for each on-disk structure. This
must match the on-disk layout, except for endianness, which is handled
by _SwapEndian methods. These structure are "plain old data" so we can
use offsetof on them. They are wrapped in an easier to use C++ API.

This resolves a lot of problems with the previous code: warnings caused
by the use of offsetof as well as a much simpler instanciation of the
objects from on-disk data.

Also fixed another problem with UUIDs, where the UUIDs were handled by
pointers in a lot of place where it was not necessary. Use references
instead. The V4 structures which don't have an UUID will return a "null"
(zero-filled) one.

Change-Id: Ifb2bf6ab94906ca50410dd3446d3566615392ca2
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6021
Reviewed-by: Raghav Sharma <raghavself28@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

xfs : version 5 superblock, checksum header file

- Implemented version 5 superblock fields and necessary macros.

- Checksum functions are implemented which will be used for crc verification and crc updates.

- fssh_kernal_priv.h ROUNDDOWN macro definition is consistent with kernal.h definition.

Change-Id: I49b7c939bfd3ea1bffc85b3db42bc678dcce75cd
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5350
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

xfs: An attempt at reading shortform dir

This patch gets read_dir, lookup and few others to work. Entries cannot
be listed yet except the root.

Change-Id: Ic4b7b61a794a1b75849e45777a383b3315b15aa8
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2915
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>

Adding superblock, types, xfs_mount and volume

Superblock work is done. A valid superblock is now detected.
xfs_shell will fail though, because the filesystem does not own it's
root node.

Change-Id: I78e3c21c4d0dd8e535fd24df4a0c107ed5fb201c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2286
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>