add ability to pass log helper as action

[bekzod]

so following is possible:

  <button {{log 'rainbow'}}>Click!</button> // logs `rainbow` and `MouseEvent` on click
  <button onclick={{log 'rainbow'}}>Click!</button> // logs `rainbow` and `MouseEvent` on click
  <button onclick={{action (log 'rainbow') 'sun'}}>Click!</button>  // logs `rainbow`,  'sun' and `MouseEvent` on click

[rwjblue]

I think we would want to leverage emberjs/rfcs#432 for this kind of thing instead.

If we went this route, we'd need an RFC to change the behavior. I'm going to close for now (in favor of either implementing emberjs/rfcs#432 or a new RFC).