[CSP] Add support for nested properties to CSP build

[SimoTod]

This PR adds a minimal enhancement to the CSP build to support nested properties via dot notation (property accessor).

<div x-data="counter">
    <button @click="foo.increment">Increment</button>
    <span x-text="foo.count"></span>
</div>

Alpine.data('counter', () => ({
    foo: {
        count: 1,

        increment() {
            this.count++
        },
    },
}))

The build size is pretty much the same and it seems a reasonable change otherwise dev using the csp build are forced to flatten the component and put all properties at the top.

I only know about one user mentioning it though so feel free to close it if you think it's not worth it for now.

[ekwoka]

Suggested change

	if (currentScope[currentExpression] === undefined) {
	if (!currentExpression in currentScope) {

should help in scenarios where the thing is expected to be undefined.

But also, this will now exhibit a different behavior than non-csp in regards to this, where it would only error when trying to access a key on the thing that is undefined, but would be happy to return undefined.

[SimoTod]

Good point, I kept the same check as the original version. Happy to change it if Caleb is cool with that.

[calebporzio]

This is great. Thanks Simone!