clang-format: Improve formatting of constructor initializers.

Before:
  Constructor()
      : aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(aaaaaaaaaaaaaaaaaaaaaaaaa(aaaa,
                                                                      aaaa)) {}
After:
  Constructor()
      : aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            aaaaaaaaaaaaaaaaaaaaaaaaa(aaaa, aaaa)) {}