fix: Add support for vite.config.ts (#6140)

TS2307: Cannot find module '@sveltejs/kit/vite' or its corresponding type declarations.

1 import { sveltekit } from "@sveltejs/kit/vite";
                            ~~~~~~~~~~~~~~~~~~~~

Found 1 error in vite.config.ts:1

.changeset/quiet-comics-crash.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Fix vite.config.ts "Cannot find module '@sveltejs/kit/vite' or its corresponding type declarations."

packages/kit/src/core/sync/write_tsconfig.js

@@ -46,7 +46,7 @@ export function write_tsconfig(config, cwd = process.cwd()) {
 	/** @param {string} file */
 	const config_relative = (file) => posixify(path.relative(config.outDir, file));
 
-	const include = ['ambient.d.ts'];
+	const include = ['ambient.d.ts', config_relative('vite.config.ts')];
 	for (const dir of [config.files.routes, config.files.lib]) {
 		const relative = project_relative(path.dirname(dir));
 		include.push(config_relative(`${relative}/**/*.js`));