feat: allow message overlay anchoring

[isekovanic]

🎯 Goal

This PR updates the message row and overlay interaction model. The message context menu now anchors its top and bottom portal items to the message bubble area instead of the full message row, and custom MessageItemView implementations can control that behavior via useMessageContext().contextMenuAnchorRef. Swipe-to-reply was also moved from the inner bubble to the full MessageItemView, while keeping the existing swipe logic intact.

As part of that cleanup, the old messageContentWidth plumbing was removed, the internal MessageBubble component was inlined into MessageItemView, and the nested messageItemView.bubble.* theme keys were flattened into top level messageItemView style keys.

🛠 Implementation details

🎨 UI Changes

iOS

Before	After

Android

Before	After

🧪 Testing

☑️ Checklist

• I have signed the Stream CLA (required)
• PR targets the develop branch
• Documentation is updated
• New code is tested in main example apps, including all possible scenarios
  • SampleApp iOS and Android
  • Expo iOS and Android

[Stream-SDK-Bot]

SDK Size

title	develop	branch	diff	status
js_bundle_size	373 KB	373 KB	0 B	🟢