fs: open: Add Truncate flag to zfs open

This commit has added new flag FS_O_TRUNC to support truncation
during file open. Modified fs_open to handle truncation based on
provided flags. Included unit tests for flag behavior with common
filesystems.

Signed-off-by: RAJAGOPALAN GANGADHARAN <g.raju2000@gmail.com>
3 files changed