Add shadow root support for isInDOM

By getting the "host" property when "parentNode" is undefined, the function can properly climb the DOM tree and allow monaco-editor to be used within a shadow root.

src/vs/base/browser/dom.ts

@@ -32,7 +32,7 @@ export function isInDOM(node: Node | null): boolean {
 		if (node === document.body) {
 			return true;
 		}
-		node = node.parentNode;
+		node = node.parentNode || node.host;
 	}
 	return false;
 }