FAT: revise using code from FreeBSD

* Rewrite most hook functions, modeling many after FreeBSD hooks and
making use of support functions ported from FreeBSD. As it stands
now, most of the FreeBS

FAT: revise using code from FreeBSD

* Rewrite most hook functions, modeling many after FreeBSD hooks and
making use of support functions ported from FreeBSD. As it stands
now, most of the FreeBSD driver files are present with minimal
changes, with a pseudo-BSD compatability layer added to make them
work in Haiku. Performance is not what it could be if the BSD code
was rewritten to interface directly with the Haiku kernel, but under
the current approach the driver might be easier to maintain in terms
of porting future FreeBSD bugfixes.
* Add support for FAT in userlandfs. Aside from being useful for
debugging, the userlandfs module provides better filename support
for characters that are not in code page 850, because it can link
libiconv.
* Update the fat_test.sh script to use dosfstools to format the tested
device, instead of the internal dosfs_initialize hook. The script
is written to test specific cluster sizes, but the initialize hook
still does not support user-specified cluster sizes.
* Coding guidelines: lightly-modified BSD files and lightly-modified
original Haiku driver files have not been revised to adhere to the
Haiku style guidelines. For BSD files, this is meant to make it
easier to compare with the FreeBSD repository when merging future
FreeBSD patches. For existing driver files, this is to highlight the
functional changes made in this change request (I can submit a
separate patch later to clean up style in these files). Also, some
#include lines are not alphbetized (they are instead ordered like
they would be in FreeBSD, because one header relies on another).

Change-Id: I92521d4b700d7aa52fe6c664cf8f83a4d9395809
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7660
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

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