Add safe string function to base lib.

Contributed-under: TianoCore Contribution Agreement 1.0

signed off by: Yao, Jiewen <jiewen.yao@intel.com>
reviewed by: Ni, Ruiyu <ruiyu.ni@intel.com>
reviewed by: Long, Qin <qin.long@intel.com>
reviewed by: Kinney, Michael D <michael.d.kinney@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdePkg@16312 6f19259b-4bc3-4df7-8a09-765794883524