feat: add array mutation methods to field arrays

[sillvva]

Fixes #14662 ("Implements")

• Adds type RemoteFormArrayFieldMethods<T> type and intersects it to RemoteFormFieldContainer and RemoteFormField
  • Adds .push(), .pop(), .unshift(), .shift(), .splice(), and .sort() methods to field arrays
• Exports RemoteFormFields type to allow the creation of custom field array wrapper functions and components
• Adds docs
• Adds test

https://stackblitz.com/edit/array-methods-308957-ddxf7li3?file=src%2Froutes%2F%2Bpage.svelte,src%2Froutes%2Ftest.remote.js,package.json

Mutating field arrays

Field arrays should have the following extra methods to mutate the array: .pop(), .push(), .shift(), .unshift(), .splice(), and .sort(). Other array methods and properties can still be accessed through the .value() method.

<script>
	import { cart } from '../data.remote';

	// add to cart
	cart.fields.items.push({
		sku: "SKU12345",
		name: "TV Set",
		price: 1200,
		quantity: 1
	});

	// remove item at index `i`
	cart.fields.items.splice(i, 1);
	
	// cart total
	cart.fields.items.value().reduce((acc, item) => acc + item.price * item.quantity, 0);
</script>

---

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[changeset-bot]

🦋 Changeset detected

Latest commit: 26e0e0c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Minor

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-14663-svelte.vercel.app/

[sillvva]

Not sure why that one test is timing out. It started after a change to the docs.