Use .?method() in more places (#152112)

Switches simple patterns like:

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

to:

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

This is more concise and avoids having to repeat the `some.thing` part

src/vs/workbench/api/common/extHostLanguageFeatures.ts

@@ -88,9 +88,7 @@ class DocumentSymbolAdapter {
 				}
 				const parent = parentStack[parentStack.length - 1];
 				if (EditorRange.containsRange(parent.range, element.range) && !EditorRange.equalsRange(parent.range, element.range)) {
-					if (parent.children) {
-						parent.children.push(element);
-					}
+					parent.children?.push(element);
 					parentStack.push(element);
 					break;
 				}