Desktop: Fix error in plugin content scripts generated with Webpack (#10680)

packages/app-desktop/gui/note-viewer/index.html

@@ -45,6 +45,9 @@
 	<script src="./scrollmap.js"></script>
 
 	<script>
+	// Fixes a warning when loading some TypeScript plugins generated with webpack.
+	window.exports = {};
+
 	// This is function used internally to send message from the webview to
 	// the host.
 	const ipcProxySendToHost = (methodName, arg) => {

packages/app-desktop/services/plugins/UserWebviewIndex.js

@@ -2,6 +2,9 @@
 const webviewApiPromises_ = {};
 let viewMessageHandler_ = () => {};
 
+// This silences a warning when running plugins generated with Webpack.
+window.exports ??= {};
+
 // eslint-disable-next-line no-unused-vars, @typescript-eslint/no-unused-vars
 const webviewApi = {
 	postMessage: function(message) {