fix: use script lang regex from svelte compiler (#1028)

Author: fehnomenal

.changeset/swift-dolphins-cheat.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+Allow script tags to span multiple lines

packages/vite-plugin-svelte/src/utils/compile.js

@@ -14,7 +14,7 @@ import { enhanceCompileError } from './error.js';
 // which is closer to the other regexes in at least not falling into commented script
 // but ideally would be shared exactly with svelte and other tools that use it
 const scriptLangRE =
-	/<!--[^]*?-->|<script (?:[^>]*|(?:[^=>'"/]+=(?:"[^"]*"|'[^']*'|[^>\s]+)\s+)*)lang=["']?([^"' >]+)["']?[^>]*>/g;
+	/<!--[^]*?-->|<script\s+(?:[^>]*|(?:[^=>'"/]+=(?:"[^"]*"|'[^']*'|[^>\s]+)\s+)*)lang=(["'])?([^"' >]+)\1[^>]*>/g;
 
 /**
  * @returns {import('../types/compile.d.ts').CompileSvelte}
@@ -172,8 +172,8 @@ export function createCompileSvelte() {
 
 		let lang = 'js';
 		for (const match of code.matchAll(scriptLangRE)) {
-			if (match[1]) {
-				lang = match[1];
+			if (match[2]) {
+				lang = match[2];
 				break;
 			}
 		}