[BUGFIX beta] Fix {{action}} helper to work with bound params.

The `{{action}}` helper will now use a non-quoted parameter and perform a bound property lookup against the action's target at the time the event is triggered.

If a non-quoted param is used, but the property lookup returns `undefined` a helpful assertion is made, and the specified parameter is used as a plain string action name (thus preventing this from breaking anyones applications).

Also, cleans up a few unrelated non-quoted uses of `{{action}}` in the test suite.

Closes #3368.