[libc++][print] Includes <format>. (#76333)

The overloads of `println` are specified in terms of `format`. The
function `format` is specified to work with ranges.

The implementations for `println` do not include `<format>`, but
libc++'s granularized header. This means the following example does not
work

  #include <vector>
  #include <print>

  int main() {
      std::vector<int> v{1, 2, 3};
      std::println("{}", v);
  }

(The other print functions also require this to work, they are specified
in terms of other format functions.)

Fixes: https://github.com/llvm/llvm-project/issues/71925