1. Show old string before enter new.
2. Enable cursor moves left or right and insert new char or remove the char before the cursor.
Signed-off-by:ydong10
Reviewed-by:lgao4
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12231 6f19259b-4bc3-4df7-8a09-765794883524