Ext4Pkg: Hide "." and ".." entries from Read() callers.

This makes it so callers that may expect FAT32 filesystems (most do)
have more normal looking ReadDir() results.
This commit also presents a better filename for files opened through
Open(".").

Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>