fix: btrfs: move accessor helpers into accessors.h (v6.2)

fix: btrfs: move accessor helpers into accessors.h (v6.2)

See upstream commit :

  commit 07e81dc94474eb62705c6f96d9ab1a5a797b8703
  Author: Josef Bacik <josef@toxicpanda.com>
  Date:   Wed Oct 19 10:51:00 2022 -0400

    btrfs: move accessor helpers into accessors.h

    This is a large patch, but because they're all macros it's impossible to
    split up.  Simply copy all of the item accessors in ctree.h and paste
    them in accessors.h, and then update any files to include the header so
    everything compiles.

Change-Id: I1f0876dd8b7a8687f6802b60c3e3baabd017cc52
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>