Only prevent default for copy paste in webviews when on electron

Fixes #106383

For web VS Code, we want the browser to handle these events instead. This means we can skip the dispatch entirely

src/vs/workbench/contrib/webview/browser/pre/host.js

@@ -111,6 +111,7 @@
 		onMessage: hostMessaging.onMessage.bind(hostMessaging),
 		ready: workerReady,
 		fakeLoad: !onElectron,
+		onElectron: onElectron,
 		rewriteCSP: onElectron
 			? (csp) => {
 				return csp.replace(/vscode-resource:(?=(\s|;|$))/g, 'vscode-webview-resource:');

src/vs/workbench/contrib/webview/browser/pre/main.js

@@ -13,6 +13,7 @@
  *   onIframeLoaded?: (iframe: HTMLIFrameElement) => void,
  *   fakeLoad?: boolean,
  *   rewriteCSP: (existingCSP: string, endpoint?: string) => string,
+ *   onElectron?: boolean
  * }} WebviewHost
  */
 
@@ -286,8 +287,14 @@
 			// make sure we block the browser from dispatching it. Instead VS Code
 			// handles these events and will dispatch a copy/paste back to the webview
 			// if needed
-			if (isCopyPasteOrCut(e) || isUndoRedo(e)) {
+			if (isUndoRedo(e)) {
 				e.preventDefault();
+			} else if (isCopyPasteOrCut(e)) {
+				if (host.onElectron) {
+					e.preventDefault();
+				} else {
+					return; // let the browser handle this
+				}
 			}
 
 			host.postMessage('did-keydown', {