Add Scrollbar to Data-Block Dropdown Pop-ups

Problem Statement Data-block dropdown menus in Blender currently lack visible scrollbars when list items exceed the viewable area, making it difficult for users to gauge the total number of items or their current position in the list. This absence forces users to scroll blindly through long lists of materials, objects, or textures without visual feedback, leading to inefficient navigation and potential oversight of available options.​

Proposed Solution Implement a persistent vertical scrollbar for all data-block dropdown pop-ups that appears whenever the content height exceeds the menu's maximum display limit. This scrollbar should follow Blender's existing UI design patterns found in the Outliner and Properties panels, supporting both visual position indication and standard click-and-drag interaction.​​

Benefits Enhanced Usability: Users can immediately identify if more items exist below the fold and gauge the list's length at a glance.

Faster Navigation: Direct interaction with a scrollbar allows for much faster traversal of large data-block collections compared to mouse-wheel scrolling alone.

UI Consistency: Aligns data-block menus with the standard scrolling behavior found throughout the rest of the Blender interface, reducing user friction