Fix IMA ad container not resizing on orientation change (iOS)

[Ibad9]

Fixes an issue https://github.com/TheWidlarzGroup/react-native-video/issues/4769 where the IMA ad container view did not resize correctly when device orientation changed on iOS.
Previously, adContainerView was initialised with a static frame (_video.bounds), so it didn’t update after rotation.

🛠️ Changes

• Replaced frame-based layout with Auto Layout constraints to pin adContainerView to _video on all edges.
• Ensures proper resizing on orientation change while retaining the existing memory leak fix.
• Tested on iOS 15.1+ (iPhone simulators) — ads now stay correctly aligned after rotation.

✅ Verification

• Verified that ads render correctly in both portrait and landscape modes.
• Confirmed no new memory leaks or constraint warnings.
• Maintains backward compatibility with existing React Native Video integrations.