ext4: Introduce a new helper function ext4_generic_write_inline_data()

ext4: Introduce a new helper function ext4_generic_write_inline_data()

A new function, ext4_generic_write_inline_data(), is introduced
to provide a generic implementation of the common logic found in
ext4_da_write_inline_data_begin() and ext4_try_to_write_inline_data().

This function will be utilized in the subsequent two patches.

Signed-off-by: Julian Sun <sunjunchao2870@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250107045549.1837589-1-sunjunchao2870@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>