Remove non-public buttonPressed: selector from broadcast picker activation (#1138)

## Summary

Apple's automated App Review flags the literal `buttonPressed:` selector
string in application binaries (ITMS-90338 / Guideline 2.5.1) and blocks
App Store submissions. Since the plugin compiles `ios/Classes/**` into
every app, any iOS app using `livekit_client` is exposed — even if it
never uses screen sharing or ReplayKit.

`BroadcastManager.showPicker(for:)` constructed and performed the
private selector to programmatically activate the system broadcast
picker (reached via `setScreenShare` → `broadcastRequestActivation`
method channel). It now activates the picker using only public API:
locate the picker's `UIButton` subview and fire it via `sendActions(for:
.touchUpInside)`. If the button is ever not found (e.g. a future OS
changes the view hierarchy), a warning is logged instead of silently
no-opping.

No API changes; runtime behavior is identical.

## Verification

- `rg buttonPressed ios/ macos/` returns no matches, so the selector
string no longer reaches downstream binaries
- `swiftc -typecheck` against the iOS simulator SDK passes for the
changed file and its dependencies

Author: hiroshihorie

.changes/broadcast-picker-private-selector

@@ -0,0 +1 @@
+patch type="fixed" "Remove non-public buttonPressed: selector from broadcast picker activation"

ios/Classes/BroadcastManager.swift

@@ -16,6 +16,7 @@
 
 import Combine
 import ReplayKit
+import UIKit
 
 @available(iOS 13.0, *)
 final class BroadcastManager {
@@ -44,8 +45,10 @@ final class BroadcastManager {
         view.preferredExtension = preferredExtension
         view.showsMicrophoneButton = false
 
-        let selector = NSSelectorFromString("buttonPressed:")
-        guard view.responds(to: selector) else { return }
-        view.perform(selector, with: nil)
+        guard let button = view.subviews.compactMap({ $0 as? UIButton }).first else {
+            print("[LiveKit] Unable to find button in RPSystemBroadcastPickerView")
+            return
+        }
+        button.sendActions(for: .touchUpInside)
     }
 }