x-bind not evaluating x-transition directive callback

[hdahlheim]

Hey Caleb, I tried to update from v2 to v3 today and noticed that x-bind does not evaluate the x-transition directive callback. It works fine when the directive value is just a string.

I get the following error using the CDN build:

cdn.js:1460 Uncaught TypeError: classString2.split is not a function
    at missingClasses (cdn.js:1460)
    at setClassesFromString (cdn.js:1468)
    at setClasses (cdn.js:1456)
    at Object.start (cdn.js:1704)
    at cdn.js:1754
    at mutateDom (cdn.js:125)
    at performTransition (cdn.js:1753)
    at transition (cdn.js:1702)
    at Object.in (cdn.js:1635)
    at HTMLDivElement.window.Element._x_toggleAndCascadeWithTransitions (cdn.js:1657)

I made a repo to demonstrate the issue with a v3 and a v2 example. In v2, it works as expected.
https://github.com/hdahlheim/alpine-v3-x-bind-transition-bug

In short, to save you a few clicks

// x-bind with directives like this works
['x-transition:enter']: "transition ease-out duration-100",

// x-bind with directives link this should work but does not
['x-transition:enter']() {
     return "transition ease-out duration-100"
},