ShellPkg: Refine code to use Strn**S safe functions instead of Str**S ones in some...

ShellPkg: Refine code to use Strn**S safe functions instead of Str**S ones in some cases.

Safe string functions may ASSERT when the source length is larger than the MaxDest. This patch use Strn**S to indicate the copy length.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Tapan Shah <<tapandshah@hp.com>>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17894 6f19259b-4bc3-4df7-8a09-765794883524