[TableGen] Introduce DagInit::getArgs that returns an ArrayRef. Use it to fix 80 column violations in arg_begin/arg_end. Remove DagInit::args and use getArgs instead. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304177 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed