Formatter: Prefer breaking before ObjC selector names over breaking at their ':'

Before:
  if ((self = [super initWithContentRect:contentRect styleMask:
                  styleMask backing:NSBackingStoreBuffered defer:YES])) {

Now:
  if ((self = [super initWithContentRect:contentRect styleMask:styleMask
                  backing:NSBackingStoreBuffered defer:YES])) {