ShellPkg: Convert all .uni files to utf-8

ShellPkg: Convert all .uni files to utf-8

To convert these files I ran:

$ python3 BaseTools/Scripts/ConvertUni.py ShellPkg

Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Shumin Qiu <shumin.qiu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19176 6f19259b-4bc3-4df7-8a09-765794883524