[0.5.x] Support Inertia transform

[timacdonald]

Fixes #70

Adds support for Inertia's transform function.

const form = useForm('post', '/register', {
    emails: ''
}).transform(data => ({
    ...data,
    emails: data.emails.split(',').map(email => email.trim()),
})

form.emails = '[email protected], [email protected]'

form.validate('emails') // { emails: ['tim@laravel.com', '[email protected]'] }
form.submit()           // { emails: ['tim@laravel.com', '[email protected]'] }

[gcaraciolo]

hey, @timacdonald. Thanks for implementing this.

[timacdonald]

No worries. Thanks for reporting the issue.