ext4: move out common parts into ext4_fallocate()

ext4: move out common parts into ext4_fallocate()

Currently, all zeroing ranges, punch holes, collapse ranges, and insert
ranges first wait for all existing direct I/O workers to complete, and
then they acquire the mapping's invalidate lock before performing the
actual work. These common components are nearly identical, so we can
simplify the code by factoring them out into the ext4_fallocate().

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20241220011637.1157197-11-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>