clang-format: [JS] Only special case top level object literal

assignments as enums.

Top level object literals are treated as enums, and their k/v pairs are put on
separate lines:

  X.Y = {
    A: 1,
    B: 2
  };

However assignments within blocks should not be affected:

  function x() {
    y = {a:1, b:2};
  }

This change fixes the second case. Patch by Martin Probst.

llvm-svn: 239462