Opt-out option for makeBindingHandlerValidatable

I would love if there was an option to opt-out of the 'hacking' of regular bindings with validation binding handlers. All it takes is put lines 46-51 of bindingHandlers.js inside a if.

My use case is that I use this validation library with property getters/setters (i.e. ko-es5) and because of this makeBindingHandlerValidatable does not work for me anyway (because it does not receive the observable object, only its value).

BTW, while I was reading this piece of code I noticed that ko.bindingHandlers.validationCore is executed in many bindings but is not the most efficient.

Why not wrap all the code inside a if (ko.validation.utils.isValidatable(observable))? If it's not true this function is a no-op. But currently it would still read the config for the element, check 3 different config settings and check the above condition 3 times :( As a side-effect it would also reduce code size.

Start in Src/bindingHandlers.js, especially lines 46-51 and the validationCore binding handler referenced in the issue. Read how makeBindingHandlerValidatable is invoked and how ko-es5 property getters/setters affect the observable argument. Done should include a clear opt-out behavior and confirmation of the requested validationCore efficiency change, with relevant existing tests updated or added.