Add screen reader support for message list

[rezabakhshilaktasaraei]

Summary

Exposes each message bubble as a virtual accessibility child, making the message history fully navigable by screen readers.

Changes (history_inner_widget.cpp/h, history_view_send_action.h)

• Overrides accessibilityChildCount(), accessibilityChildName(), accessibilityChildRect(), accessibilityChildState(), accessibilityChildRole(), and column sub-item methods.
• Each message becomes a ListItem with a detailed description:
  • Sender name (or "Me"), forwarded-from, reply-to context
  • Message text content with custom emoji descriptions
  • Media metadata: photo/video dimensions, file name/size, audio artist/title/duration
  • Status: seen/not seen, played/not played, edited, pinned, views count
  • Reactions list, via-bot attribution, post signature
  • Web page preview: site name, title, description
  • Poll: question, options, vote count, status
  • Contacts, locations, stickers, games, invoices, gifts, giveaways, todo lists
• 46 multi-column sub-items for structured per-field screen reader access
• Fires accessibilityChildFocused() on keyboard navigation.
• Keyboard context menu (Applications / Shift+F10) now correctly targets the accessibility-focused message instead of the last mouse-hovered message.
• Arrow key navigation now scrolls to keep the focused message visible.
• PageUp/PageDown support for jumping through messages by one page height.
• Focused message index is now tracked by item pointer (_accessibilityFocusedItem) and revalidated when the list changes (new messages, deletions, history loading), preventing stale index references.

Dependencies

• Requires lib_ui#278 for Accessible::Item infrastructure.

New lang keys

~80 new lng_sr_message_* keys + shared delivery status keys (lng_sr_chat_sending/sent/failed/received).

Test plan

• Navigate message list with arrow keys — screen reader announces sender, text, media info, and status
• Verify forwarded messages, replies, and web previews are announced correctly
• Verify media messages report type, dimensions, file size, duration as applicable
• Verify hit-testing: clicking a message with screen reader cursor selects it
• Open context menu with Applications key or Shift+F10 — menu actions (reply, edit, etc.) target the focused message, not the last mouse-hovered one
• Navigate up/down with arrow keys past the visible area — view scrolls to keep the focused message on screen
• Use PageUp/PageDown to jump through messages by one visible page
• Receive new messages while navigating — focused message stays correct after list changes