clang-format: Fix C99 designated initializers corner cases

Summary:
This fixes the missing space before the designated initializer when `Cpp11BracedListStyle=false` :

  const struct A a = { .a = 1, .b = 2 };
                      ^

Also, wrapping between opening brace and designated array initializers used to have an excessive penalty (like breaking between an expression and the subscript operator), leading to unexpected wrapping:

  const struct Aaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaa =
      {[1] = aaaaaaaaaaaaaaaaaaaaaaaaaaa,
       [2] = bbbbbbbbbbbbbbbbbbbbbbbbbbb};

instead of:

  const struct Aaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaa = {
      [1] = aaaaaaaaaaaaaaaaaaaaaaaaaaa,
      [2] = bbbbbbbbbbbbbbbbbbbbbbbbbbb};

Finally, designated array initializers are not binpacked, just like designated member initializers.

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, krasimir, klimek

Differential Revision: https://reviews.llvm.org/D33491

llvm-svn: 305696