Implement directory-iteration for the ext4l filesystem driver, allowing
callers to iterate through directory entries one at a time.
Add ext4l_opendir() which opens a directory and returns a stream handle,
ext4l_readdir() which returns the next directory entry, and
ext4l_closedir() which closes the stream and frees resources.
The implementation uses a struct dir_context to capture single entries
from ext4_readdir(), with logic to skip previously returned entries
since the htree code may re-emit them.
Update struct file to include a position.
Wire these functions into fs_legacy.c for the ext4l filesystem type.
Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
b9558d8a06