iomap: pass more arguments using the iomap writeback context

Add inode and wpc fields to pass the inode and writeback context that
are needed in the entire writeback call chain, and let the callers
initialize all fields in the writeback context before calling
iomap_writepages to simplify the argument passing.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/20250710133343.399917-3-hch@lst.de


Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>