ShellPkg/redirection: Insert \xFEFF for ENV variable redirection
ShellPkg/redirection: Insert \xFEFF for ENV variable redirection

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1080

Per Shell spec 2.2 chapter 3.4.4.2, Unicode file tag should be
inserted in the output from the input redirected variable, to ensure
it looks like a UCS-2 encode file.

The patch fixes this issue.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <9fa3a6894a36bca79e6a72ad65af5a5702efecd1@intel.com>
Reviewed-by: Jaben Carsey <2d4ee76b36e91bee3a58378b7538904eb027a616@intel.com>

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2