MdePkg\Library\UefiFileHandleLib: Make FileHandleWriteLine support both ASCII and...

MdePkg\Library\UefiFileHandleLib: Make FileHandleWriteLine support both ASCII and UNICODE file.

When the file is a UNICODE file (with UNICODE file tag) write UNICODE text.
When the file is an ASCII file write ASCII text.
If the file size is zero (without the file tag at the beginning) write ASCII text as default.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17701 6f19259b-4bc3-4df7-8a09-765794883524