Currently it's a weak point in Blender, that users cannot access the object dimensions more easily. Currently we hide this inside the 3D View Sidebar. For such a basic and useful concept as setting the dimensions, I would like this to be more apparent in the UI, and also discourage opening the Sidebar just for this one item.
To make the Transform panel more useful and consistent, this patch adds Dimensions to the Object Transform panel.
Rather than doing it the naive way of just adding more controls, this patch adds an enum, matching the rotation mode enum.
This is similar to how we allow users to both use Field of View and also millimetres to describe the camera focal length:
Transform set to Factor (Default)
Transform set to Dimensions: