Add StrnSizeS() and AsciiStrnSizeS() APIs. These 2 safe version APIs are used to replace StrSize() and AsciiStrSize(). Those two APIs use similar checks as [Ascii]StrnLenS(). Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Hao Wu <hao.a.wu@intel.com> Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>