[cleanup] Run clang-format over most of YAMLParser.h to fix a bunch of
small formatting inconsistencies with the rest of LLVM and even this
file. I looked at all the changes and they seemed like just better
formatting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206209 91177308-0d34-0410-b5e6-96231b3b80d8