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])) {




git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172333 91177308-0d34-0410-b5e6-96231b3b80d8