MdePkg: Make the FileHandleGetFileName return the file name in right format.

1. If the file is not a directory remove the redundant '\' char in file name string returned from UefiFileHandleLib.FileHandleGetFileName.
2. Update function comments.

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@18314 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Include/Library/FileHandleLib.h

@@ -356,7 +356,9 @@ FileHandleSetSize (
 
 /**
   Function to get a full filename given a EFI_FILE_HANDLE somewhere lower on the
-  directory 'stack'.
+  directory 'stack'. If the file is a directory, then append the '\' char at the 
+  end of name string. If it's not a directory, then the last '\' should not be 
+  added.
 
   @param[in] Handle             Handle to the Directory or File to create path to.
   @param[out] FullFileName      Pointer to pointer to generated full file name.  It