clang-format: [ObjC+JS] Allow bin-packing of array literals.

After reading the style guides again, they don't actually say how to
pack or not pack array literals. Based on some user reports, array
initializers can unnecessarily get quite long if they contain many
small elements. Array literals with trailing commas are still formatted
one per line so that users have a way to opt out of the packing.

Before:
  var array = [
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa,
    aaaaaa
  ];

After:
  var array = [
    aaaaaa, aaaaaa, aaaaaa, aaaaaa, aaaaaa, aaaaaa, aaaaaa, aaaaaa, aaaaaa,
    aaaaaa, aaaaaa
  ];

llvm-svn: 257615