Bot API 8.0+ bug: event fullscreenChanged isn't being fired

[kubk]

Steps to reproduce:

1. Add the following code:

WebApp.onEvent("fullscreenChanged", () => {
  console.log('fullscreenChanged');
});

2. Click on Settings > Fullscreen

Expected result:

• Callback for fullscreenChanged is fired
• WebApp.isFullscreen becomes true

Actual result:

• Callback for fullscreenChanged isn't fired
• WebApp.isFullscreen stays false even in fullscreen

Note: the subscription code above is correct because when I switch from fullscreenChanged to ⁠viewportChanged, the callback is triggered. However, even in this case, ⁠WebApp.isFullscreen remains false.