fix: use esnext for useVitePreprocess (#452)

Author: bluwy

.changeset/cuddly-tools-fold.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+Use esnext for useVitePreprocess

packages/vite-plugin-svelte/src/utils/preprocess.ts

@@ -23,6 +23,7 @@ function createViteScriptPreprocessor(): Preprocessor {
 		if (!supportedScriptLangs.includes(lang)) return;
 		const transformResult = await transformWithEsbuild(content, filename, {
 			loader: lang as ESBuildOptions['loader'],
+			target: 'esnext',
 			tsconfigRaw: {
 				compilerOptions: {
 					// svelte typescript needs this flag to work with type imports