clang-format: Prefer column layout if possible.

Add a severe penalty for not using column layout for braced lists. If
there are solutions with column layout, these are generally preferable
over bin-packed solutions.

Before:
  std::vector<MyValues> aaaaaaaaaaaaaaaaaaa{ aaaaaaa, aaaaaaaaaa, aaaaa,
                                             aaaaaaaaaaaaaaa, aaa, aaaaaaaaaa, a,
                                             aaaaaaaaaaaaaaaaaaaaa, aaaaaaaaaaaa,
                                             aaaaaaaaaaaaaaaaaaa +
                                                 aaaaaaaaaaaaaaaaaaa,
                                             aaaaaaa, a };
After:
  std::vector<MyValues> aaaaaaaaaaaaaaaaaaa{
    aaaaaaa,      aaaaaaaaaa,
    aaaaa,        aaaaaaaaaaaaaaa,
    aaa,          aaaaaaaaaa,
    a,            aaaaaaaaaaaaaaaaaaaaa,
    aaaaaaaaaaaa, aaaaaaaaaaaaaaaaaaa + aaaaaaaaaaaaaaaaaaa,
    aaaaaaa,      a
  };

llvm-svn: 195546