Merge patch series "Avoid filesystem references to writeback internals"

Kundan Kumar <kundan.kumar@samsung.com> says:

The series introduces writeback helper APIs and converts f2fs, gfs2
and nfs to stop accessing writeback internals directly.

As suggested by Christoph [1], filesystem code that directly accesses
writeback internals is split out:
[1] https://lore.kernel.org/all/20251015072912.GA11294@lst.de/

* patches from https://patch.msgid.link/20260213054634.79785-1-kundan.kumar@samsung.com:
  nfs: stop using writeback internals for WB_WRITEBACK accounting
  gfs2: stop using writeback internals for dirty_exceeded check
  f2fs: stop using writeback internals for dirty_exceeded checks
  writeback: prep helpers for dirty-limit and writeback accounting

Link: https://patch.msgid.link/20260213054634.79785-1-kundan.kumar@samsung.com
Signed-off-by: Christian Brauner <brauner@kernel.org>