Add ability to display all clips in a playlist as a tiled contact sheet

[mvineeta]

RPA sessions support playlists, each containing multiple clips. Currently, we use RV’s Sequence mode to play clips linearly and have a side-by-side comparison mode for comparing two playlists.

This request proposes a Contact Sheet Mode — similar in spirit to side-by-side mode — but instead of comparing two playlists, it would tile all clips from a single selected playlist in a grid view.

🎯 Feature Request:

Add a "Contact Sheet" mode for playlists that:

• Displays all clips in a playlist tiled in a grid (e.g., 2x2, 3x3, etc.)
• Each tile shows a frame (by default, first or representative frame)
• Should be toggled via a button, shortcut, or menu option (e.g., next to Sequence/Stack mode)
• Grid layout may be auto-computed or user-defined (e.g., based on number of clips)

✅ Expected Behavior:

On entering Contact Sheet mode:

• Viewer tiles all clips in the current playlist into a grid layout.
• If user switches playlist, the contact sheet updates accordingly.

📌 Notes:

This feature is similar to the existing side-by-side comparison mode between two playlists, but now applied to all clips within a single playlist for contact sheet-style visualization.
Please investigate to see if we can make use of the existing "OpenRV Layout mode" to handle the grid layout and rendering, ensuring consistency and reusing tested functionality.