Add a scroll bar to the bottom of the left control panel (render controls)

The render preview makes use of this, so why should not the controls also do so? This would be useful in the event a user must access a control while still viewing the whole render preview at full resolution, which may require the panel to be partially collapsed.

Locate the left control panel for the render controls and compare it with the render preview's existing scrollbar behavior. Confirm that the controls can scroll independently while the full-resolution render preview remains visible, including when the panel is partially collapsed.

Written by the indexing model from the issue text.