Use optional chaining for more method calls (#156938)

This rewrites code such as:

```ts
if (thing) {
    thing.method();
}
```

To the more concise:

```ts
thing?.method();
```

This was done using a simple find replace. I tried to keep the change pretty conservative so it only touches simple cases like above

src/vs/base/browser/dom.ts

@@ -1149,9 +1149,7 @@ export function removeTabIndexAndUpdateFocus(node: HTMLElement): void {
 	// in the hierarchy of the parent DOM nodes.
 	if (document.activeElement === node) {
 		const parentFocusable = findParentWithAttribute(node.parentElement, 'tabIndex');
-		if (parentFocusable) {
-			parentFocusable.focus();
-		}
+		parentFocusable?.focus();
 	}
 
 	node.removeAttribute('tabindex');