Add "defaults" method to Form helper

[claudiodekker]

This PR adds a "defaults" method to the Form Helper, allowing people to reset the default values without initializing the form. Do note that it does not reset the form, but only changes the defaults that are used when the form (or some of it's fields) are reset.

Signatures:

setDefaults()
setDefaults(field: string, value: string)
setDefaults(fields: object)

Here's some examples of how you can use this:

Vue 2 / Vue 3

export default {
  data() {
    return {
      form: this.$inertia.form({
        email: 'johndoe@example.com',
        password: 'secret',
        remember: false,
      }),
    }
  },
  methods: {
    submit() {
      this.form.post('/login', {
        onSuccess: () => {
          // Set the current values as the new defaults
          this.form.defaults()

          // Only change the email field
          this.form.defaults('email', 'foo@example.com')

          // Change the defaults to multiple fields
          this.form.defaults({
            email: 'bar@example.com',
            password: 'hunter2',
          })
        },
      })
    },
  },
}

React

const { post, setDefaults } = useForm({
  email: 'johndoe@example.com',
  password: 'secret',
  remember: true
});

post('/login', {
  onSuccess: () => {
    // Set the current values as the new defaults
    setDefaults()

    // Only change the email field
    setDefaults('email', 'foo@example.com')

    // Change the defaults to multiple fields
    setDefaults({
      email: 'bar@example.com',
      password: 'hunter2',
    })
  }
}

Svelte

const form = useForm({
  email: 'johndoe@example.com',
  password: 'secret',
  remember: false,
})

function login() {
  $form.post(route('login.store'), {
    onSuccess: () => {
      // Set the current values as the new defaults
      $form.defaults()

      // Only change the email field
      $form.defaults('email', 'foo@example.com')

      // Change the defaults to multiple fields
      $form.defaults({
        email: 'bar@example.com',
        password: 'hunter2',
      })
    }
  })