MdePkg/Library/UefiFileHandleLib: Make FileHandleReadLine return the right buffer...

MdePkg/Library/UefiFileHandleLib: Make FileHandleReadLine return the right buffer size.

1. '\r' char will not return in buffer so buffer size should exclude the number of '\r' char.
2. When 'Truncate' is TRUE return the truncated string with 'EFI_SUCCESS' status.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18276 6f19259b-4bc3-4df7-8a09-765794883524