[bug]Inability to close screen sharing in iOS example

[AoEiuV020]

Describe the bug

After enabling screen sharing in the iOS example, it cannot be properly closed.

Upon investigation, it appears that iOS screen sharing cannot be terminated directly through code. Following Jitsi's approach, when a user clicks to stop screen sharing, a system dialog should appear (similar to the one shown when starting screen sharing, but with a "Stop Broadcast" button).

Testing showed that calling BroadcastManager().requestActivation(); works, but there's uncertainty about the most appropriate placement for this code. If placed in the example, it would expose the BroadcastManager and create an inconsistency where starting screen sharing works normally but stopping requires special handling, which seems counterintuitive.

To Reproduce

1. Launch the iOS example app
2. Enable screen sharing
3. Attempt to close screen sharing by clicking the close button
4. Observe that while the screen sharing status in the meeting stops, the system still shows the broadcast as active, and an error message "Screen sharing stopped" suddenly appears after a few seconds.

Expected behavior

When the screen sharing close button is clicked, a system dialog should appear with a "Stop Broadcast" button, allowing the user to properly terminate the screen sharing session.

Platform information

• Flutter version: 3.35.1
• Plugin version: 2.5.0
• Flutter target OS: iOS
• Flutter target OS version: 18
• Flutter console log: