ShellPkg: Refactor string manipulation in UefiShellLib command

ShellPkg: Refactor string manipulation in UefiShellLib command

This patch replaces StrCpy with StrnCpy or refactors out the usage of StrCpy through some other means.
This patch replaces StrCat with StrnCat or refactors out the usage of StrCat through some other means.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Erik Bjorge <erik.c.bjorge@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15839 6f19259b-4bc3-4df7-8a09-765794883524