Merge patch series "iomap: misc buffered write path cleanups and prep"

Brian Foster <bfoster@redhat.com> says:

Here's a bit more fallout and prep. work associated with the folio batch
prototype posted a while back [1]. Work on that is still pending so it
isn't included here, but based on the iter advance cleanups most of
these seemed worthwhile as standalone cleanups. Mainly this just cleans
up some of the helpers and pushes some pos/len trimming further down in
the write begin path.

The fbatch thing is still in prototype stage, but for context the intent
here is that it can mostly now just bolt onto the folio lookup path
because we can advance the range that is skipped and return the next
folio along with the folio subrange for the caller to process.

[1] https://lore.kernel.org/linux-fsdevel/20241213150528.1003662-1-bfoster@redhat.com/

* patches from https://lore.kernel.org/20250506134118.911396-1-bfoster@redhat.com:
  iomap: rework iomap_write_begin() to return folio offset and length
  iomap: push non-large folio check into get folio path
  iomap: helper to trim pos/bytes to within folio
  iomap: drop pos param from __iomap_[get|put]_folio()
  iomap: drop unnecessary pos param from iomap_write_[begin|end]
  iomap: resample iter->pos after iomap_write_begin() calls

Link: https://lore.kernel.org/20250506134118.911396-1-bfoster@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>