Implement a tiny expression parser to improve formatting decisions.

With this patch, the formatter introduces 'fake' parenthesis according
to the operator precedence of binary operators.

Before:
return aaaa & AAAAAAAAAAAAAAAAAAAAAAAAAAAAA || bbbb &
       BBBBBBBBBBBBBBBBBBBBBBBBBBBBB || cccc & CCCCCCCCCCCCCCCCCCCCCCCCCC ||
       dddd & DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD;
f(aaaaaaaaaaaaaaaaaaaa && aaaaaaaaaaaaaaaaaaaa, aaaaaaaaaaaaaaaaaaaa &&
  aaaaaaaaaaaaaaaaaaaa, aaaaaaaaaaaaaaaaaaaa && aaaaaaaaaaaaaaaaaaaa);

After:
return aaaa & AAAAAAAAAAAAAAAAAAAAAAAAAAAAA ||
       bbbb & BBBBBBBBBBBBBBBBBBBBBBBBBBBBB ||
       cccc & CCCCCCCCCCCCCCCCCCCCCCCCCC ||
       dddd & DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD;
f(aaaaaaaaaaaaaaaaaaaa && aaaaaaaaaaaaaaaaaaaa,
  aaaaaaaaaaaaaaaaaaaa && aaaaaaaaaaaaaaaaaaaa,
  aaaaaaaaaaaaaaaaaaaa && aaaaaaaaaaaaaaaaaaaa);

Future improvements:
- Get rid of some of the hacky ways to nicely format certain constructs.
- Merge this parser and the AnnotatingParser as we now have several parsers
  that analyze (), [], etc.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174714 91177308-0d34-0410-b5e6-96231b3b80d8