Ext4Pkg: Add symbolic links support

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3677



Provided support for symlink file type. Added routine which allows
reading and following them through recursive open() call. As a security
meausure implemented simple symlink loop check with nest level limit
equal 8. Also this patch moves Ext4Open functionality to internal
routine.

Cc: Marvin Häuser <mhaeuser@posteo.de>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Vitaly Cheptsov <vit9696@protonmail.com>
Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
Reviewed-by: Pedro Falcato <pedro.falcato@gmail.com>