ShellPkg: Fix command line parsing for script files (%1, %1, etc...)

This change makes sure that all script files get their command lines properly parsed for use in the script file.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15103 6f19259b-4bc3-4df7-8a09-765794883524