fix: locate Rollup annontaion friendly to JS downgraders (#17724)

Closes #17722
Looks like after downgrading `?.`, `/* @__PURE__ */` may happen in an
invalid location.

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

.changeset/icy-otters-fall.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: locate Rollup annontaion friendly to JS downgraders

packages/svelte/src/internal/client/constants.js

@@ -67,7 +67,10 @@ export const STALE_REACTION = new (class StaleReactionError extends Error {
 	message = 'The reaction that called `getAbortSignal()` was re-run or destroyed';
 })();
 
-export const IS_XHTML = /* @__PURE__ */ globalThis.document?.contentType?.includes('xml') ?? false;
+export const IS_XHTML =
+	// We gotta write it like this because after downleveling the pure comment may end up in the wrong location
+	!!globalThis.document?.contentType &&
+	/* @__PURE__ */ globalThis.document.contentType.includes('xml');
 export const ELEMENT_NODE = 1;
 export const TEXT_NODE = 3;
 export const COMMENT_NODE = 8;

packages/svelte/src/internal/client/dom/reconciler.js

@@ -2,15 +2,15 @@
 
 import { create_element } from './operations.js';
 
-const policy = /* @__PURE__ */ globalThis?.window?.trustedTypes?.createPolicy(
-	'svelte-trusted-html',
-	{
+const policy =
+	// We gotta write it like this because after downleveling the pure comment may end up in the wrong location
+	globalThis?.window?.trustedTypes &&
+	/* @__PURE__ */ globalThis.window.trustedTypes.createPolicy('svelte-trusted-html', {
 		/** @param {string} html */
 		createHTML: (html) => {
 			return html;
 		}
-	}
-);
+	});
 
 /** @param {string} html */
 function create_trusted_html(html) {