Use optional method calls in more places (#151634)

This replaces code like:

```ts
if (foo.bar) {
    foo.bar(cat);
}
```

with:

```ts
foo.bar?.(cat)
```

Which is more concise but has the same meaning

src/vs/workbench/api/test/common/testRPCProtocol.ts

@@ -57,9 +57,7 @@ export class TestRPCProtocol implements IExtHostContext, IExtHostRpcService {
 	private set _callCount(value: number) {
 		this._callCountValue = value;
 		if (this._callCountValue === 0) {
-			if (this._completeIdle) {
-				this._completeIdle();
-			}
+			this._completeIdle?.();
 			this._idle = undefined;
 		}
 	}