Add the top section of the "what's new modal" (title and top image) as items in the RecyclerView so that the entire content is scrollable

[catalinradoiu]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1211724162604201/task/1212974313804261?focus=true

Description

Refactored the remote messaging cards list UI to use a more flexible adapter pattern. The main changes include:

• Created a new ModalListItem sealed class to represent different types of items in the list (Header and CardListItem)
• Moved the header view from the main layout into a separate recyclerview item
• Updated the adapter to handle the new item types
• Simplified the view layout by removing redundant constraints and barriers
• Added proper image loading with success/failure callbacks inside the new view holder
• Improved the scrolling behavior by using the recyclerview for all content (therefore improving UX when having a longer list of items)

Steps to test this PR

Check the steps in this task and make sure that the scenarios below are working as expected:

• Verify that the header displays correctly with both local and remote images
• Confirm that card items render properly in the list
• Check that scrolling works smoothly through the entire content
• Ensure all action buttons function as expected

UI changes

Before	After
what_new_non_scrollable.mp4 (uploaded via Graphite)	whats_new_scrollable.mp4 (uploaded via Graphite)

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Note

Makes the entire modal scrollable and simplifies rendering by treating the header as a list item.

• Introduces ModalListItem (Header and CardListItem) and updates CardsListAdapter to render the header via a new ViewHolder with Glide image loading and success/failure callbacks
• Refactors CardsListRemoteMessageViewModel to build modalListItems and expose primaryAction/primaryActionText; fires pixels on header image load and item visibility/clicks
• Simplifies view_cards_list_remote_message.xml by removing embedded header; adds view_remote_message_header.xml for the header row
• Updates CardsListRemoteMessageView to submit modalListItems and wire header image callbacks; replaces old header handling
• Expands unit tests to cover new state shape, image file usage, actions, and pixel firing

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[catalinradoiu]

• Adjust “What's new” modal UI and items for tablet #7605
• Add the top section of the "what's new modal" (title and top image) as items in the RecyclerView so that the entire content is scrollable #7588 👈 (View in Graphite)
• develop

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[anikiki]

Looks good and works as expected! 🎉