feat: added live preview svelte package

[PeteJStewart]

Live Preview Package | Svelte

This is the live preview package for Svelte. Similar to the Vue & React Live Preview packages.
There are details about implementing the package within the README file. In general I have tried to keep it as close to the Vue implementation as possible.

The simplest example of how it can be used is:

<script lang="ts">
  import type { PageProps } from './$types';
  import { useLivePreview } from '@payloadcms/live-preview-svelte';
  import { readable } from 'svelte/store';
  import { PUBLIC_PAYLOAD_URL } from '$env/static/public';

  let { data }: PageProps = $props();
  let article = useLivePreview(data, {
    serverURL: PUBLIC_PAYLOAD_URL,
  });
</script>

<article>
	<h1>{$article.title}</h1>
	<div>{@html $article.content}</div>
</article>

I've tried to keep the DX as clean as possible and to replicate all feature found in the Vue package.
useLivePreview also returns loading as a readable rune, but in most cases it's not needed.
There is further information about that in the README.

There have been some discussions about this on Discord: https://discord.com/channels/967097582721572934/967097582721572937/1366094097890279515

What?

New Svelte Live Preview package

Why?

Because there wasn't one, and many people use Svelte and want this package.

How?

The package uses the @payloadcms/live-preview package and Svelte writable/readable store to extract the logic to a library package.

[jacobsfletch]

Thanks for this @PeteJStewart! I made a few changes here, namely:

1. Added the live-preview-svelte package to the list of acceptable commit scopes in .github/workflows/pr-title.yml
2. Added it to the scripts property in the root package.json
3. Aliased the path to the package in the paths property in the root tsconfig.base.json
4. Added a reference to the package in the root tsconfig.json
5. Added the package to the publish list in tools/releaser/src/lib/publishList.ts

Another change that is needed here is that docs need to go into the /docs/live-preview directory instead of the README. Can you do this?

Beyond that I'm hoping we can have a few Svelte developers test out a canary before it is released, but unfortunately I cannot publish a pre-release from your fork. I'll look into this, but we may have to open a PR from a direct branch instead, or mark as beta.

[PeteJStewart]

Thanks @jacobsfletch, I'll add the docs tomorrow and remove the README. 👍

[PeteJStewart]

@jacobsfletch I believe this PR is ready now. I've added the Svelte documentation to /docs/live-preview.
I haven't removed the README, as I felt the extra info in there was useful, however, feel free to remove it if you want to keep the directory clean.
I personally like to see README files with the code, as I'm often looking at the code rather than the documentation, so it's nice to find some docs there, too. But I appreciate that's not the normal setup on Payload.