Add defaults() to Core validator + React/Vue Inertia implementation

[pascalbaljet]

This PR adds a defaults() function to the Core validator so that you can pass a data object as new defaults.

The passed data replaces the underlying initialData and oldData, which are used to determine whether a field should be validated, and when resetting a field.

The react-inertia and vue-inertia packages are updated as well to take advantage of the new validator.defaults() function. It now calls defaults() on both Inertia's useForm() helper, as well as the Precognition validator.

import { useForm } from 'laravel-precognition-vue-inertia'

const form = useForm('post', '/register', {
    name: 'John',
})

form.defaults({ name: 'Jane' })

form.name = 'John'
form.reset()

console.log(form.name) // Outputs: 'Jane'

I've added additional tests for core and vue-inertia. There wasn't a test suite for react-inertia, so I ported the tests from the Vue package.