Add Netlify Functions Context to Netlify Adapter (#4145)

* Add Netlify Functions Context to Netlify Adapter

* change to patch and update readme

* fix lint

* Update packages/adapter-netlify/README.md

* Update many-pigs-deliver.md

Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/many-pigs-deliver.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-netlify': patch
+---
+
+Add Netlify Functions context as `event.platform.context`

packages/adapter-netlify/README.md

@@ -57,7 +57,9 @@ During compilation, redirect rules are automatically appended to your `_redirect
 
 ### Using Netlify Functions
 
-[Netlify Functions](https://docs.netlify.com/functions/overview/) can be used alongside your SvelteKit routes. If you would like to add them to your site, you should create a directory for them and add the configuration to your `netlify.toml` file. For example:
+With this adapter, SvelteKit endpoints are hosted as [Netlify Functions](https://docs.netlify.com/functions/overview/). Netlify function handlers have additional context, including [Netlify Identity](https://docs.netlify.com/visitor-access/identity/) information. You can access this context via the `event.platform.context` field inside your hooks and endpoints.
+
+Additionally, you can add your own Netlify functions by creating a directory for them and adding the configuration to your `netlify.toml` file. For example:
 
 ```toml
 [build]

packages/adapter-netlify/src/handler.js

@@ -9,8 +9,8 @@ import { split_headers } from './headers';
 export function init(manifest) {
 	const server = new Server(manifest);
 
-	return async (event) => {
-		const rendered = await server.respond(to_request(event));
+	return async (event, context) => {
+		const rendered = await server.respond(to_request(event), { platform: { context } });
 
 		const partial_response = {
 			statusCode: rendered.status,